Delete the selected area
by pushing the Delete key, or the Edit->Clear menu. You now
have only the image left.
This selection will now be used to create a layer mask for this
layer. Next, click on the Layer->Add Layer Mask->Hide
Selection menu item. Since only the background was selected, this
function will create a layer mask that reveals only the part of the
layer that contains the image.
Click on the next layer up. This should select the next layer and
show it at the same time. Repeat this process starting with the
"Magic Wand" tool again. As you proceed to each layer, you will
see your mosaic start to come together!