Are you asking why a GIF is used, or why the 43 bytes are needed?
I think a GIF is likely the smallest wide-supported resources format (force the browser request a URL to load a specific resource). The 43 bytes is the minimum size for a valid GIF, so the browser won't log an error loading the image and go through all load events.
I think a GIF is likely the smallest wide-supported resources format (force the browser request a URL to load a specific resource). The 43 bytes is the minimum size for a valid GIF, so the browser won't log an error loading the image and go through all load events.
It looks like in modern browsers it's 35 bytes: https://stackoverflow.com/a/15960901/407650