You just drag the photo or texture to the picture area in the middle of the frame. The frame is copyable so if you drag it out of your inventory, you'll have a "clean" copy still there in case you break the rez'd copy.
If you would like any of these customized with names at the top, or an On Touch chat message, IM me in-world. These services are not free but very reasonable.
These frames are resizeable, so they can fit on a table top or be enlarged for a wall.
If you find your photos don't fit into the photo area properly, no worries. If you turn the frame around, or look in the back, you'll see that the photo prims are a different color. Right click the frame and select Edit. Then click Edit Linked Parts, and select the prim you want to modify. You can then check the Stretch option and proceed to make the photo prim the size you need it to be.