Evening out lighting.

The fragment of the illustration peeking out from the green panel suggests that making a selection of the currently hidden image would be the primary challenge. I suggest that, in order to preserve the element you have hidden, the Blend if command with a blank layer below the image. Once cleared, it can be filled with your chosen flat color. (if necessary, depending on the density of the the now-hidden folder element, it may be masked to silhouette and placed on an added layer.)

Depending how complex the image is, the quickest way may be just to mask the image using select and mask then place a color fill layer behind it

Dave

I’d start with using Adobe Camera Raw’s Vignette option to help even out the all of your raw shots (you can sync the vignette to all images). If you only shot JPEG, then you could try using the ACR filter or processing the JPEG files in ACR. There are Photoshop methods, however the better the source image the less work to do in Photoshop. The green redaction box does not help interested parties much though.