Sorry, must be missing something.Long press on the home screen or you can go to gallery and set it.
Open the gallery, open your picture, click on settings for that picture (three bars on the upper right corner), set picture as, wallpaper. You can then crop or stretch the box on the image.
Sent from my Nexus 7 using Android Central Forums
My photos are in the Dropbox app but I dont see a way to get them to the gallery
