If you get the file downloaded, can you apply for instance, photoshop to the image and try to "undo" it by using your icons and thus see the changes?
No, that will not work unless you have the working file and the program that created the file.
The finished file, usually a JPEG, is flat.
What is the best or close to it way to spot a "photoshopped" picture/image?
It helps if you've done a few
Look for density variations within the pic. Mismatched shadows, blurring, errors in perspective. Cloned areas, blend marks. Digital fuzz, noise.
All shopped pics have errors. The more the orignal is altered the more errors there are bound to be.
If you want more detail then I will explain indepth off board (nobody here cares).
It's funny and just struck me that we cannot believe 100% any image we see on line.
don't be slow. You can't believe 100% of anything anywhere.