'Why statistics tools use GIF to send request?

Analysis tools use GIF to send statistics data like this

var img1 = new Image();
img1.src = 'http://path/to/file.gif?otherinfohere';

I know using image to send request can avoid browser ban script running and GIF file has the smallest size.

But why not just sending an empty response, our target is sending statistics data after all, nobody care what will be received,isn’t it ?

Sources

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