Not really that huge of a problem. When making requests you also usually send a header which includes the user agent.
The program just logs how many times the image has been requested and it reads the user agent data. No Javascript is actually executed.
Well it might be possible to have a XSS somehow but I haven’t really done much research into this possibility.
In general it’s a pretty standard way of handling embedded images. Email does this too. That’s how you have these services that can check if someone read a mail