Recreating uploads/linked images with imagecreatefrom* php

User uploaded images account for a large portion of the content on the site I'm working on. I tried storing them outside of the webroot and fetching them with readfile() for security reasons, but it was just too slow so I had to go back to the old method.

Now I'm looking to make sure all uploads are 100% sanitized since they'll be stored inside the webroot. My question is, if a user were to rename a harmful script to a .jpg, .gif, .png, or .bmp and uploaded it, would it still be harmful when executed or fetched if the image was recreated with a function like this:

function imageCreateFromAny($filepath) { 
    $type = exif_imagetype($filepath); // [] if you don't have exif you could use getImageSize() 
    $allowedTypes = array( 
        1,  // [] gif 
        2,  // [] jpg 
        3,  // [] png 
        6   // [] bmp 
    ); 
    if (!in_array($type, $allowedTypes)) { 
        return false; 
    } 
    switch ($type) { 
        case 1 : 
            $im = imageCreateFromGif($filepath); 
        break; 
        case 2 : 
            $im = imageCreateFromJpeg($filepath); 
        break; 
        case 3 : 
            $im = imageCreateFromPng($filepath); 
        break; 
        case 6 : 
            $im = imageCreateFromBmp($filepath); 
        break; 
    }    
    return $im;  
} 

In other words, is there anyway to trick one of the imagecreatefrom* functions into executing content as a script instead of an image or would even a harmful script that's been run through this be reduced to a broken image?