Best way to cache resized images using PHP and MySQL

Question

What would be the best practice way to handle the caching of images using PHP.

The filename is currently stored in a MySQL database which is renamed to a GUID on upl

Answer 1

Instead of keeping the file address in the db I prefer adding a random number to the file name whenever the user logs in. Something like this for user 1234: image/picture_1234.png?rnd=6534122341

If the user submits a new picture during the session I just refresh the random number.

GUID tackles the cache problem 100%. However it sort of makes it harder to keep track of the picture files. With this method there is a chance the user might see the same picture again at a future login. However the odds are low if you generate your random number from a billion numbers.