Why would you want to do this. It would better just to scan the picture. You will lose detail if you want to convert it to film because you would essentially have to just take a picture of it.
Wow. I didn't think people did this... but I guess you have the right reason... You know what this sounds like...? "Have sex... to SAVE the friendship... "
Back in the days before digital photos and digital projectors a friend of mine used to do this a lot. Take prints and make them into slides for presentations. There was a set up at our local library (not in Houston) where you mounted the print on a board of some sort, and took a picture of it. There was a tripod involved, and it was done in a quasi darkroom type place so there was no glare. I didn't notice any real quality issues on projections that were about 15 feet high. I don't know if those set ups still exist. You could always try something similar by printing your photo's and then photographing them.
