Working with images and transparency

kmwsuvball,

As I (mis)understand it, you need to have a transition from full opacity to full transparency in a curved band, more or less horizontal at the lower left and to the top near the upper right corner.

If that is the case, and if you can cut off the leftmost part of the couple image outside the front image, you can do it with a(n Opacity) Mask as follows, Smart Guides being your friends:

1) With the Pen Tool, draw a stroke/nofill curve of the front image where you wish to have full transparency (the couple being fully clear) from the left side to the top side (snap to both) along one of the lines in the image (this can be done with one or two intermediate Anchor Points with Handles, you can adjust later), then Click the top left corner of the front image, then Click at the starting point to close the path; the adjustment can be done with the Direct Selection Tool;

2) Create a corresponding closed path path with a curve where you wish to have full opacity along another line (or more crudely just use Offset Path, it can go outside the top and left side of the front image);

3) Select the path from 1) and hold Ctrl/Cmd while you press C then F then X then F to bring it to the front;

4) Select the path from 1)/3) and switch from stroke to a (fully) black fill, then selæect the path from 2 and switch from stroke to a white fill;

5) Select both paths and Object>Blend>Option and apply Smooth Color and Align to Path, then Object>Blend>Make;

6) Hold Shift and Click the front image, then apply Make (Opacity) Mask in the Transparency panel;

7) Mask out the leftmost part of the couple image.

This ought to give you a clear upper left part of the couple image with a transition to the front image.

You can look into the terms and ways by a search here (empty search, just ignore the error message and insert search terms):

https://helpx.adobe.com/search-results.html?q=&scope=%5B%22helpx%22%5D&subscope=%5B%5D&limit=10&start_index=0&sort_orderby=relevancy&sort_order=desc&post_facet_filters=%7B%22applicable_products%22%3A%5B%5D%7D

As you said, your image is transparent, there's art in the area you want to be clear, you'll need a clipping mask to isolate the art you want, or take it in to PS and erase the area you want to be clear.

You may find playing with opacity will give you a pleasing result (and/or the transparency modes) without having to do that work...