Take a close look at the bottom of your wine glass. Does it have a completely flat bottom or does it curve up towards the center and stem? You'll want to be careful to apply decoupage glue only to the portion of the glass that will touch the photo. (ie. The flat part.)
Go ahead and use your brush to apply decoupage glue sparingly to the flat parts of the bottom of your glass! It'll dry faster and clearer if you don’t put too much on.
Once you've covered the surface, attach your photo face up.