Image protection/easy display

[bit bit spears]

Hi, I have an account with WIREIMAGE, and they have this file ~> PreviewPopImg.asp?img=2398429384 or whatever, and I would like pictures to appear that way. Like, so they won't be able to find the original source for the picture. Because, the pic site am running will require an account, and people can easily hack it by right-clicking on the thumbnail and pasting that url into the address bar, and take off "thumb_" and then you have the pic! I was wandering if you could do that with php. For example, i saw the watermark thread 'logo.php?img=384928' like that, but so it wouldn't show the directory like it does-or the file name, like producing a whole new picture!:)

What should I do??

[bit bit spears]

also, could you have it so this would happen~> when people are not logged in or whatever, they can view the images, but they will show up watermarked, and then also, could you have a button that says 'download image' or whatever that would download it ONLY if you were logged in?