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

After searching for a while, I've found the answer. The browser didn't cached anything (and didn't send the If-Modified-Since) until I sent the following header:

Cache-Control: private;

After doing this all worked fine.