Probably Programming

Yesterday I was base64-encoding an image so I could send it to CouchDB to test some code I’m working on for a client. It reminded me of something I did a while back to set cookies on a remote server.

Basically, a small PHP script was put on the remote server which took a couple of GET parameters and set some cookies based on their values. The script then output a 1×1 transparent GIF. A PHP script on the local server generated an IMG tag which linked to this image and set the parameters based on the COOKIES on the local server.

This process also had to happen in the reverse direction, so I had to send the script to developers on the other side. I wanted to keep it as simple as possible, so I put the actual image contents in the PHP file as a base64 encoded string. I used the GIMP to generate the smallest transparent GIF I could manage so there wouldn’t be too huge of a nasty string in the file. I came up with something like the following:

< ?php
setcookie('foo', $_GET['foo']);
header('Content-Type: image/gif');
echo base64_decode('R0lGODlhAQABAIABAP///wAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==');
?>

Remembering this got me to wondering, how small could you make a GIF? The file generated by the GIMP was only 43 bytes, but it seemed to be that you should be able to make a file which is representing a single pixel a bit smaller than that.

So, with equal parts of determination and derangement, I set about finding out.

Though of somewhat dubious usefulness, I managed to generate a perfectly valid GIF of only 26 bytes in length, which has the potential to display completely differently in various different software.

Read on to see how I found my way to this point.

(more…)