
Now, open the image on Photoshop. (File » Open)
Make sure you make the bg transparent if its not already. To do this, simply Duplicate the existing layer (Layer » Duplicate layer), get your Magic Wand tool (
) and click on the white space in the background.
Now push the backspace button on your keyboard. Last, using your layer module, right-click the BG and select 'Delete'.

Lastly, go to Edit » Define Pattern. Name it whatever you wish & you're done. Now you've got a spiffy new pattern to appy to all your images!! :]