Good idea, but it won't work. The Hubble optics aren't made to focus at a close object like Earth's Moon.

Hubble cam image 1/10 of an arcsecond (one degree is 3600 arcseconds). If Hubble was pointed t the Earth it could in theory resolve objects of 30 cm, about 1 foot. The problem is the image wouldn't be in focus and the Earth is so bright that it would permanently damage Hubble's instruments, as they are made to pick-up very faint objects.

The (sorta) good news is that there is a "Hubble Telescope" that looks at the Earth everyday. It is called the KH-11 and is a U.S. Spy satellite that has operated for over 30 years. Its telescope and cameras are much more advanced than Hubble's and it is 100% made just to look at Earth, although it optimized for a narrow view.

Good luck getting an image though. The last guy who leaked a picture of (a now old) Russian Aircraft Carrier, that was under construction went to federal prison for 16 years. This image was likely taken by a KH-8 or 9 and not the then new KH11.