For those looking to grab the resolution of a JPEG image without using GD nor ImageMagic... I wrote this simple function.

Too bad GD doesn't have this very simple function for us to use...

<?php
function getJPEGresolution($filename){
    $outRez=array();
    // Read the file
    ob_start(); // start a new output buffer
    $image   = file_get_contents($filename);
    
    // grab DPI information from the JPG header
    $outRez["xDPI"] = ord($image[15]);
    $outRez["yDPI"] = ord($image[17]);
    ob_end_clean(); // stop this output buffer

    //xDPI and yDPI should equal in value... but we output both anyway...
    return($outRez);
}//end function getJPEGresolution
?>