Straighten multiple layers inside photoshop

Let's assume that this is a collage of four scans. The script expects to receive each scan as a separate open documents:

I assume that on each scan the film crosses the frame horizontally (although a small inaccuracy is allowed here). First of all, I apply a threshold to the image to get contrasting edges (BORDER_THRESHOLD = 100). Then I take two narrow stripes from the image at the top and bottom with a small indent from the edge (BORDER_OFFSET = 0.03, i.e. 3% of the frame height):

The script analyzes each strip, expecting to encounter a film border on its way. We consider the border to be the moment when there are at least 10 black pixels in a row on the left (BORDER_LEFT_GAIN = 10), and at least 5 on the right (BORDER_RIGHT_GAIN = 5). The 4 points found allow us to determine the object's borders, as well as the angle of rotation (we ignore the bend).  Accordingly, we crop and rotate the image.

Next we try to find the borders of each frame. I decided to use perforation (since it is clearly visible and clean enough):

To do this, I draw a vertical line 22% of the image width from the left (PERFORATION_OFFSET = 0.22), apply a slightly more aggressive threshold to make them sharper (PERFORATION_THRESHOLD = 165) and move vertically I find closed circles of perforation assuming that its width is more than 20 pixels (PERFORATION_GAIN = 20) and I will not encounter a single black pixel before its border (unfortunately, if the perforation is dirty, this can be a problem)

In this case, you either need to change the PERFORATION_THRESHOLD threshold value, or manually paint over the dirt with a white brush.
If everything went well, then we calculate the distance between the perforation centers and take them as the frame height. All that remains is to split the image vertically into separate frames, taking into account the found size (the script tries to save the extreme upper and extreme lower frames if they are visible at least by 80% (FRAME_OVERLAP = 0.8)). Each frame is saved in the same folder where the original image is located with the addition of a numerical index.

I can't guarantee that the script will work properly on other images (there are too many things that can go wrong), but maybe this will help.

const BORDER_RIGHT_GAIN = 40,
    BORDER_LEFT_GAIN = 70,
    PERFORATION_GAIN = 124,
    NOISE_GAIN = 10,
    BORDER_THRESHOLD = 130,
    PERFORATION_THRESHOLD = 165,
    PERFORATION_OFFSET = 0.22,
    BORDER_OFFSET = 0.1,
    FRAME_OVERLAP = 0.8,
    REVERSE_FRAMES = true;
var apl = new AM('application'),
    doc = new AM('document'),
    lr = new AM('layer');
try {
    if (apl.getProperty('numberOfDocuments')) activeDocument.suspendHistory('Save Frames', 'main()')
}
catch (e) { alert('An error has occurred! Too many things can go wrong') }
function main() {
    var hst = activeDocument.activeHistoryState;
    var bounds = getObjectBounds(BORDER_THRESHOLD);
    doc.makeSelection(bounds[0], bounds[1], bounds[2], bounds[3]);
    doc.crop()
    lr.duplicateLayer()
    lr.convertToSmartObject()
    lr.rotate(bounds[4])
    lr.revealAll();
    lr.selectLayer('backwardEnum')
    lr.fill('white')
    lr.selectLayer('forwardEnum')
    lr.flatten();
    var bounds = getObjectBounds(BORDER_THRESHOLD);
    doc.makeSelection(bounds[0], bounds[1], bounds[2], bounds[3]);
    doc.crop();
    var result = getFramesDimensions(PERFORATION_THRESHOLD);
    var docRes = doc.getProperty('resolution'),
        docW = doc.getProperty('width') * docRes / 72,
        docH = doc.getProperty('height') * docRes / 72,
        height = 0,
        title = doc.getProperty('title').replace(/\..+$/, ''),
        pth = doc.getProperty('fileReference').path;
    for (var i = 0; i < result.length - 2; i++) { height += result[i + 1][0] - result[i][0] }
    height += result[result.length - 1][0] - result[result.length - 2][0];
    height = height / (result.length - 1);
    var offset = (result[result.length - 1][0] + result[result.length - 1][1] / 2 + height) - docH,
        i = result.length - 1;
    if (offset < height - (height * FRAME_OVERLAP)) {
        doc.resizeCanvas(offset, 'top')
        var top = result[i][0] + result[i][1] / 2;
        doc.makeSelection(top, 0, top + height, docW)
        saveLayer(new File(pth + '/' + title + '_' + (REVERSE_FRAMES ? result.length : 0)))
    }
    for (i--; i >= 0; i--) {
        var top = result[i][0] + result[i][1] / 2;
        doc.makeSelection(top, 0, top + height, docW)
        saveLayer(new File(pth + '/' + title + '_' + (REVERSE_FRAMES ? i + 1 : result.length - 1 - i)))
    }
    var offset = -((result[0][0] + result[0][1] / 2) - height);
    if (offset < height - (height * FRAME_OVERLAP)) {
        doc.resizeCanvas(offset, 'bottomEnum')
        doc.makeSelection(0, 0, height, docW)
        saveLayer(new File(pth + '/' + title + '_' + (REVERSE_FRAMES ? 0 : result.length - 1 - i)))
    }
    activeDocument.activeHistoryState = hst;
    return;
    function getObjectBounds(threshold) {
        var docRes = doc.getProperty('resolution'),
            docW = doc.getProperty('width') * docRes / 72,
            docH = doc.getProperty('height') * docRes / 72,
            hst = isolateLayer(threshold),
            line1 = getX(Math.ceil(docH * (BORDER_OFFSET)), hst),
            line2 = getX(Math.ceil(docH * (1 - BORDER_OFFSET)), hst);
        doc.close();
        doc.deleteLayer();
        return [0, Math.min(line1[0], line2[0]), docH, Math.max(line1[1], line2[1]), Math.atan2(line2[0] - line1[0], docH * (1 - BORDER_OFFSET) - docH * (BORDER_OFFSET)) * 180 / Math.PI]
        function getX(top, historyBackup) {
            lr.makeSelection(top, 0, top + 1, docW);
            doc.crop();
            var f = new File(Folder.temp + '/colors.raw');
            doc.saveToRAW(f)
            activeDocument.activeHistoryState = historyBackup;
            var colors = readStrip(f);
            f.remove();
            return [findCoordinate(colors, BORDER_LEFT_GAIN), docW - findCoordinate(colors.reverse(), BORDER_RIGHT_GAIN)];
        }
    }
    function getFramesDimensions(threshold) {
        var docRes = doc.getProperty('resolution'),
            docW = doc.getProperty('width') * docRes / 72,
            docH = doc.getProperty('height') * docRes / 72,
            hst = isolateLayer(threshold),
            sel = Math.ceil(docW * (PERFORATION_OFFSET));
        lr.makeSelection(0, sel, docH, sel + 1)
        doc.crop();
        var f = new File(Folder.temp + '/colors.raw');
        doc.saveToRAW(f)
        var colors = readStrip(f);
        f.remove();
        doc.close();
        lr.deleteLayer();
        return findPerforation(colors, PERFORATION_GAIN);
    }
    function isolateLayer(threshold) {
        lr.flatten();
        lr.duplicateLayer();
        lr.convertToSmartObject();
        lr.editSmartObject();
        lr.threshold(threshold);
        lr.convertToGrayscale();
        return activeDocument.activeHistoryState
    }
    function saveLayer(f) {
        lr.duplicateLayer()
        lr.convertToSmartObject()
        lr.editSmartObject();
        doc.saveACopyToTGA(24, f)
        doc.close()
        doc.deleteLayer()
    }
}
function readStrip(f) {
    var content = '';
    if (f.exists) {
        f.open('r');
        f.encoding = "BINARY";
        content = f.read();
        f.close();
        f.remove();
        var colors = function (s) {
            var m = 0, c = [];
            for (var i = 0; i < s.length; i++) {
                var k = s.charCodeAt(i); m += k; c.push(k)
            };
            return c
        }(content);
        return colors;
    }
}
function findCoordinate(s, threshold) {
    for (var i = 0; i < s.length; i++) {
        if (s[i] > 128) continue;
        if (readWithOffset(s.slice(i), threshold)) return i
    }
    return -1
    function readWithOffset(s, threshold) {
        for (var i = 0; i < s.length; i++) {
            if (i > threshold) return true
            if (s[i] > 128) return false;
        }
    }
}
function findPerforation(s, threshold) {
    s.reverse()
    for (var i = 0; i < s.length; i++) {
        if (s[i] > 128) { s[i] = 0; continue; }
        if (s[i] < 128) break;
    }
    s.reverse()
    for (var i = 0; i < s.length; i++) {
        if (s[i] > 128) continue;
        if (s[i] < 128) break;
    }
    var objects = [];
    for (var i; i < s.length; i++) {
        if (s[i] < 128) continue;
        var result = readWithOffset(s.slice(i));
        if (result > threshold) {
            i = i + result;
            objects.push([i - (result + 1), result])
        }
    }
    return objects
    function readWithOffset(s) {
        for (var i = 0; i < s.length; i++) {
            if (s[i] < 128) {
                if (endOfPerforation(s.slice(i))) {
                    return i
                }
                else {
                    i += (s.length > NOISE_GAIN ? NOISE_GAIN : s.length)
                }
            }
        }
    }
    function endOfPerforation(s) {
        var len = s.length > NOISE_GAIN ? NOISE_GAIN : s.length
        for (var i = 0; i < len; i++) {
            if (s[i] > 128) return false;
        }
        return true;
    }
}
function AM(target) {
    var s2t = stringIDToTypeID,
        t2s = typeIDToStringID;
    target = target ? s2t(target) : null;
    this.getProperty = function (property, id, idxMode) {
        property = s2t(property);
        (r = new ActionReference()).putProperty(s2t('property'), property);
        id != undefined ? (idxMode ? r.putIndex(target, id) : r.putIdentifier(target, id)) :
            r.putEnumerated(target, s2t('ordinal'), s2t('targetEnum'));
        return getDescValue(executeActionGet(r), property)
    }
    this.hasProperty = function (property, id, idxMode) {
        property = s2t(property);
        (r = new ActionReference()).putProperty(s2t('property'), property);
        id ? (idxMode ? r.putIndex(target, id) : r.putIdentifier(target, id))
            : r.putEnumerated(target, s2t('ordinal'), s2t('targetEnum'));
        return executeActionGet(r).hasKey(property)
    }
    this.duplicateLayer = function () {
        executeAction(s2t("copyToLayer"), undefined, DialogModes.NO);
    }
    this.convertToSmartObject = function () {
        executeAction(s2t("newPlacedLayer"), undefined, DialogModes.NO);
    }
    this.editSmartObject = function () {
        executeAction(s2t("placedLayerEditContents"), new ActionDescriptor(), DialogModes.NO);
    }
    this.convertToGrayscale = function () {
        (d = new ActionDescriptor()).putClass(s2t("to"), s2t("grayscaleMode"));
        executeAction(s2t("convertMode"), d, DialogModes.NO);
    }
    this.makeSelection = function (top, left, bottom, right) {
        (r = new ActionReference()).putProperty(s2t("channel"), s2t("selection"));
        (d = new ActionDescriptor()).putReference(s2t("null"), r);
        (d1 = new ActionDescriptor()).putUnitDouble(s2t("top"), s2t("pixelsUnit"), top);
        d1.putUnitDouble(s2t("left"), s2t("pixelsUnit"), left);
        d1.putUnitDouble(s2t("bottom"), s2t("pixelsUnit"), bottom);
        d1.putUnitDouble(s2t("right"), s2t("pixelsUnit"), right);
        d.putObject(s2t("to"), s2t("rectangle"), d1);
        executeAction(s2t("set"), d, DialogModes.NO);
    }
    this.flatten = function () {
        executeAction(s2t("flattenImage"), new ActionDescriptor(), DialogModes.NO);
    }
    this.threshold = function (level) {
        (d = new ActionDescriptor()).putInteger(s2t("level"), level);
        executeAction(s2t("thresholdClassEvent"), d, DialogModes.NO);
    }
    this.crop = function () {
        (d = new ActionDescriptor()).putBoolean(s2t("delete"), true);
        executeAction(s2t("crop"), d, DialogModes.NO);
    }
    this.saveToRAW = function (f) {
        (d = new ActionDescriptor()).putBoolean(s2t('copy'), true);
        (d1 = new ActionDescriptor()).putObject(s2t("as"), s2t("rawFormat"), d);
        d1.putPath(s2t("in"), f);
        executeAction(s2t("save"), d1, DialogModes.NO);
    }
    this.close = function (saving) {
        saving = saving ? saving : 'no';
        (d = new ActionDescriptor()).putEnumerated(s2t("saving"), s2t("yesNo"), s2t(saving));
        executeAction(s2t("close"), d, DialogModes.NO);
    }
    this.selectLayer = function (order) {
        (r = new ActionReference()).putEnumerated(s2t("layer"), s2t("ordinal"), s2t(order));
        (d = new ActionDescriptor()).putReference(s2t("null"), r);
        executeAction(s2t("select"), d, DialogModes.NO);
    }
    this.fill = function (color) {
        (d = new ActionDescriptor()).putEnumerated(s2t("using"), s2t("fillContents"), s2t(color));
        d.putEnumerated(s2t("mode"), s2t("blendMode"), s2t("normal"));
        executeAction(s2t("fill"), d, DialogModes.NO);
    }
    this.revealAll = function () {
        executeAction(s2t("revealAll"), new ActionDescriptor(), DialogModes.NO);
    }
    this.resizeCanvas = function (height, order) {
        (d = new ActionDescriptor()).putBoolean(s2t("relative"), true);
        d.putUnitDouble(s2t("height"), s2t("pixelsUnit"), height);
        d.putEnumerated(s2t("vertical"), s2t("verticalLocation"), s2t(order));
        d.putEnumerated(s2t("canvasExtensionColorType"), s2t("canvasExtensionColorType"), s2t("white"));
        executeAction(s2t("canvasSize"), d, DialogModes.NO);
    }
    this.saveACopyToTGA = function (bitDepth, pth) {
        (d1 = new ActionDescriptor()).putInteger(s2t("bitDepth"), bitDepth);
        (d = new ActionDescriptor()).putObject(s2t("as"), s2t("targaFormat"), d1);
        d.putPath(s2t("in"), pth);
        d.putBoolean(s2t("copy"), true);
        d.putEnumerated(s2t("saveStage"), s2t("saveStageType"), s2t("saveSucceeded"));
        executeAction(s2t("save"), d, DialogModes.NO);
    }
    this.deleteLayer = function () {
        (r = new ActionReference()).putEnumerated(s2t('layer'), s2t('ordinal'), s2t('targetEnum'));
        (d = new ActionDescriptor()).putReference(s2t("null"), r);
        executeAction(s2t("delete"), d, DialogModes.NO);
    }
    this.rotate = function (angle) {
        (r = new ActionReference()).putEnumerated(s2t("layer"), s2t("ordinal"), s2t("targetEnum"));
        (d = new ActionDescriptor()).putReference(s2t("null"), r);
        d.putEnumerated(s2t("freeTransformCenterState"), s2t("quadCenterState"), s2t("QCSAverage"));
        d.putUnitDouble(s2t("angle"), s2t("angleUnit"), angle);
        d.putEnumerated(s2t("interfaceIconFrameDimmed"), s2t("interpolationType"), s2t("bicubic"));
        executeAction(s2t("transform"), d, DialogModes.NO);
    }
    function getDescValue(d, p) {
        switch (d.getType(p)) {
            case DescValueType.OBJECTTYPE: return { type: t2s(d.getObjectType(p)), value: d.getObjectValue(p) };
            case DescValueType.LISTTYPE: return d.getList(p);
            case DescValueType.REFERENCETYPE: return d.getReference(p);
            case DescValueType.BOOLEANTYPE: return d.getBoolean(p);
            case DescValueType.STRINGTYPE: return d.getString(p);
            case DescValueType.INTEGERTYPE: return d.getInteger(p);
            case DescValueType.LARGEINTEGERTYPE: return d.getLargeInteger(p);
            case DescValueType.DOUBLETYPE: return d.getDouble(p);
            case DescValueType.ALIASTYPE: return d.getPath(p);
            case DescValueType.CLASSTYPE: return d.getClass(p);
            case DescValueType.UNITDOUBLE: return (d.getUnitDoubleValue(p));
            case DescValueType.ENUMERATEDTYPE: return { type: t2s(d.getEnumerationType(p)), value: t2s(d.getEnumerationValue(p)) };
            default: break;
        };
    }
}