searching for and replacing base64 image string with php

I have an HTML string that am getting from the database. The string has several base64 images that i need to replace with an image file which am supposed to generate from the base64 image string. I have no idea how i can do this. Any pointers will be highly appreciated.

original html

intended html

Answer

echo preg_replace_callback('#((?!src=)[^>])*?src=")data:image/(gif|png|jpeg);base64,([\w=+/]++)("[^>]*>)#', "data_to_img", $content);

function data_to_img($match) {
    list(, $img, $type, $base64, $end) = $match;

    $bin = base64_decode($base64);
    $md5 = md5($bin);   // generate a new temporary filename
    $fn = "tmp/img/$md5.$type";
    file_exists($fn) or file_put_contents($fn, $bin);


    return "$img$fn$end";  // new  tag
}