PHP image comparison

Question

img_1 is created by PHP and img_2 is saved on server. I'm trying to compare those to images to see if they're different, I tried this but it doesn't work.

$script_img = imagecreatetruecolor(2390, 2400);
$web_img = imagecreatefrompng("URL_TO_IMG");

if ($script_img==$web_img ) {
    echo "SAME";
}
else{
    echo "DIFFERENT";
}

Next example works but when I call imagepng PHP creates image in browser or weird letters (if headers isn't set to image/png) and I don't want that.

$script_img = imagecreatetruecolor(2390, 2400);
$web_img = imagecreatefrompng("URL_TO_IMG");
$rendered = imagepng($web_img);

if ($script_img==$rendered ) {
    echo "SAME";
}
else{
    echo "DIFFERENT";
}

I also tried file_get_contents($script_img) == file_get_contents("URL_TO_IMG") but it doesn't work.

Using md5(file_get_contents(imagecreatetruecolor(2390, 2400))) == md5(file_get_contents(imagecreatefrompng("URL_TO_IMG"))) works but I doubt that is the best/correct way to compare 2 images.

What is the best/correct way to compare images in PHP?

http://stackoverflow.com/questions/3270929/compare-2-images-in-php — Mohammad, Jun 18 '16 at 11:34
I already fount that answer but I'm interested what is the correct way to compare images — ihh66042, Jun 18 '16 at 11:40
First you need to very specifically define what you think entails two images being "equal". This is a very commonly discussed issue, [edit] your question to include your research. — CodeCaster, Jun 18 '16 at 11:41
Take img_1 and copy paste it and rename it to img_2. Now we have 2 equal images. — ihh66042, Jun 18 '16 at 11:42
So you're only interested in a byte-for-byte equal image file? Then a hash of the file is fine. — CodeCaster, Jun 18 '16 at 11:44
Yes, I want to compare files not image "look". Ok, thank you — ihh66042, Jun 18 '16 at 11:52

score 0 · Accepted Answer · answered Jun 18 '16 at 11:36

0

Why don't you try comparing MD5 Hash of the two images.

  $md5LocalImg = md5(file_get_contents($script_img));
  $md5WebImg   = md5(file_get_contents($web_img));
  if ( $md5LocalImg == $md5WebImg ){
     echo("SAME");
  }
  else{
    echo("DIFFERENT");
  }

answered Jun 18 '16 at 11:36

eracube

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This works but I doubt that this is the correct way to compare images – ihh66042 Jun 18 '16 at 11:39
I depends upon your requirement. You can use some image processing libraries if you want to go ahead with processing those images. Otherwise MD5 hash does the job. – eracube Jun 18 '16 at 11:43

PHP image comparison

1 Answers1