1. A method for verifying registration of images of an internal anatomic target obtained using a first imaging system and a second imaging system, the method comprising: (a) acquiring a first image of the anatomic target and at least a portion of a third imaging system using the first imaging system; (b) measuring a distance between the third imaging system and the anatomic target using the third imaging system; (c) acquiring a second image of the anatomic target using the second imaging system; (d) registering the first image and the second image using the registration; and (e) based on (i) positions of the at least a portion of the third imaging system and the anatomic target in the first image and (ii) the measured distance, computing an error in the registration.