At one point I was messing around with mixed media and silver gelatin fiber based photos. I too noticed a problem with getting the photo to stick down once i started adding the other mediums. One option that worked for me was to take the back layer of the photograph off. By rewetting the photo and carefully pulling off a layer of the paper worked....but it was time consuming.
You could also try printing on a single weight paper.
I would suggest trying Foma natural-base paper. The surface is not at all glossy, and has a pretty heavy matte surface. Given the feel of the surface, I have to believe that it is very porous.
It is nice to see this thread still active! Christine, my only experience in "pealing" a fiber based paper was such a disaster I didn't think to try it again. I will try again (and hopefully learn how to keep the image in one rather than 4 pieces). Dan, unfortunately one of the papers I was having trouble with was Foma FB Natural.
The technique of drymounting the print to a sheet of absorbent art paper (BFK) before adding it to the collage is working great. That really has solved my "the back of the print won't stick to wax" problem. In addition, encaustics can get rather thick (dimensional), so having the paper backing actually helps "raise" the photo closer to the surface in many situations.
I've found I can get very good adhesion on the front of the photo by starting with a bit of air gun heating and lighter first coats and then good air gun "fusing" between coats. The front is much easier (more receptive to the wax) than the back.
Now, my biggest problem is that I'm not that good a painter and encaustics are a difficult medium....... I hate it when the technical problems are solved and there is nothing left to blame but...... ME!