Blank image encoded as data-uri

I looked into it and the smallest possible transparent GIF image, encoded as a data-uri, was this:

data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==

which is what I'm using now.

If you need a transparent image 1x1 pixel, just set this data uri as src default attribute (keep the /// parts, it encodes byte 255, not a comment).

data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==

This is instead a base64 encoding for an image 1x1 white.

data:image/gif;base64,R0lGODlhAQABAIAAAP7//wAAACH5BAAAAAAALAAAAAABAAEAAAICRAEAOw==

Otherwise you could set data:null and save ~60 extra bytes for each image.