I have a few online arty friends and we are swapping 5x7 ATC's. I have been experimenting with image transfer, using Berol Marvin Medium. These have worked quite well but need patience and if you wet them too much they get sticky on the front side. So I had several failures.
Method is to photocopy the original design, then paint the Marvin Medium on the front. Two coats were needed, with 2 days drying time between coats. Then another two days to cure. You then wet the back of the image and rub off the paper. You are left with a transparent image, sometimes better than others.
These are the ATC's I made using pages from Dombey and Son by Charles Dickens, published by Chapman Hall, published 1886 (the book is in very poor condition so I felt it was ok to break it up). Images stuck on with Atelier Binder medium. Top coat Gloden Tar Gel and I used acrylic paints. The cut out flowers from the paper have also been stuck on in some of the images. Two paintings have been cut up, both on 140lb water colour paper.