After reading http://dsecrg.com/files/pub/pdf/XSS_in_images_evasion_bypass_(eng).pdf, it is clear that allowing image uploads from users opens you to XSS attacks.
I wasn't able to find any PHP examples of how to screen an uploaded image for XSS attacks.
I found one for CodeIgniter, which I am using. The function is xss_clean($file, IS_IMAGE), but there is only 1 sentence of documentation for it, so I have no idea how it works and a comment in their forum said it had an unreasonably high rate of false positives, so it's not usable in production.
What do you recommend to prevent XSS attacks within an uploaded image?