You can't.
There is no DRM for images - all you can do is watermark images so they are unusable, but once you issue images in electronic format there is no electronic way to protect them, only legal methods such as licensing and lawyers!
There are plans to add DRM to JPG format:
DRM Could Be Added to the JPEG Image Format[
^] but to be honest, I woudln't hold your breath waiting for it. Plus, movies and CDs have had DRM for many years, and we all know how well that works in preventing illegal copies appearing on the internet! :laugh:
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