munge / obfuscate ?

Hi All, I have written an app to allow a person to go online and see a picture we take of them. When we link to the picture I don't want it to be obvious that the URL is Domain.Com/Pix/123.jpg because the next person we take a picture of may be 123.jpg, so I am trying to munge/obfuscate the URL to make it less obvious. Of course coders can figure it out, but we just want to keep out the normal people. Does someone have an obfuscate function which still allows the URL to work, but doesn't allow the person to figure it out? Thanks!