Why serve 1x1 pixel GIF (web bugs) data at all?

Question

Many analytic and tracking tools are requesting 1x1 GIF image (web bug, invisible for the user) for cross-domain event storing/processing.

Why to serve this GIF i

Answer 1

This is to answer the OP's question - "why to serve GIF image data..."

Some users will put a simple img tag to call your event logging service -

In this case, if you don't serve an image, the browser will show a placeholder icon that will look ugly and give the impression that your service is broken!

What I do is, look for the Accept header field. When your script is called via an img tag like this, you will see something like following in the header of the request -

Accept: image/gif, image/*
Accept-Encoding:gzip,deflate
...

When there is "image/"* string in the Accept header field, I supply the image, otherwise I just reply with 204.