Image Max URL does not contain any form of telemetry. No usage is tracked.

By default, it will check for updates every day. This is done using the Github API. The only personally identifiable information transmitted to Github is your user-agent string (browser version and OS information). You can disable this by going to the extension options, and disabling "Check for updates" under the Updates section of the General tab.

This extension, like many others, might lead to websites being able to more accurately fingerprint you. I am not personally aware of any websites actively doing this, but please keep in mind that this extension could be detected by a website.