Test for and grab user edited thumbnail

I’m trying to test for and grab user edited thumbnails but only if they are user edited. I have a set “add_image_size” parameter in my functions file that I’d want to use for some images that don’t get cropped funky by the automatic job that WordPress does upon upload.

Is there a way to test if an image has been custom cropped, scaled or edited in any way and then use that image or am I stuck just grabbing the default thumbnail no matter what and having it show the user edited image if it finds that?

EDITED: To clarify a bit further, I know I can just use the ‘thumbnail’ size and that will automatically get either the user edited thumbnail or the default one that WordPress creates. The issue is that it limits the amount of different thumbnail sizes one can use on the site. So maybe the real question is:

Is there a way to add another radio button option to the Image Editor to apply it to registered custom sizes?