Open the first image
in Photoshop by clicking "File", then "Open", and browsing to it.
Double-click it to open it in your workspace.Open the second image by repeating the process, which will cause it to tile on top of the other image.Click
the "Select" menu at the top of the screen, then choose "All". Press
the "Ctrl" and "C" keys to invoke the copy function. Click back to the
first image, then press "Ctrl" and "V" together on your keyboard to
paste the second image directly on top. Click the "Move" tool, which
looks like a black arrowhead with a cross mark, on the "Tools" palette,
then drag the imported images into place.