adhesive photos

[Willem]

I make my paintings by glueing photos onto hardboard covered with gesso,and then interconnecting the pictures with oil paint. Anyway, a photo store recommended 3M photomount adhesive. It works for a while, but then the edges come loose. So, what is the right adhesive to use? Alternatively
I could treat the oil painting and pictures with a varnish. Maybe that
holds better. Any suggestions?

Thanks

[RSD99]

One suggestion would be to 'seal' the hardboard with a high quality varnish
before anything else is applied.