I'd love to hear thoughts on this, too. I tried using the xyron and the image looked dull/matte looking through the glass.
My streaks remind me of a "ghost" leftover of a bubble that has been pressed out from between the photo and back of the pendant. They're kind of long oval shaped, and I always have them when I put the photo on the back.
Recently I gave up and started using the xyron to attach the photo to the front of the pendant, and use Colores Doming Resin on the top and painted on the sides. I've tried to attach a photo of what mine look like on top