Caching image requests through PHP - If-Modified-Since not being sent

Question

I am serving images through php and having some problems setting it up to respond with 304 headers to save on load time.

Most of the code below I found on php.net. I

Answer 1

I had to use Keith's solution with combination of azkotoki's and Zsolti's posts above to make everything work as required.

so, final example would be: