Loading external images will reveal to the site where it’s loaded from at least these things:

• User’s IP
• Useragent string
• Referrer

Also it can set third-party cookies which can be used to track specific user.

I don’t know if this project processes any of that data, but outside images can be used for tracking purposes.

At least it would be a good idea to limit some of this things for that img tag by setting some attributes that prevent referrer and cookies from being sent.