Proof of purchase system to make it easier

My clients are getting hit with complaints regarding usage of photographs more frequently now. So far, so good. I take a screenshot showing I purchased the image, but I'd like a way to categorize all the images I purchased by client so I can take a picture of the whole bunch together or, better yet, be able to download proof of purchase issued by Adobe. I now have about 50 pages I have to scroll through to find one image and it's pretty annoying. If there's a simpler way, someone please tell me!