I'm obsessed with photo jewellery and there is no cure.
The rings & cabochons were from a German shop on Dawanda, in case you're wondering.
Here's what you need.
Cut out a snippet from a magazine in the matching size of your cabochon.
Glue it in the photo place of the ring.
Wait a little, maybe 20 minutes, then drip a tiny ball of glue on the pic and quickly put the cabochon on it, gently pressing all glue bubbles out.
I used a peg to hold it together over night, to avoid any bubbles that could appear later. :)