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 believe it should be

if (isset($headers['If-Modified-Since']) && (strtotime($headers['If-Modified-Since']) >= $file_time)) {

Checking if the modified time is greater than or equal rather than just equal. Although I do understand the two values should be the same.