Embodiments facilitate in-time registration of temporally separated image acquisition sessions to obtain highly comparable images without physical restraint of the camera and/or subject. For example, while displaying a live view being acquired of a subject in real time in a viewfinder window of an image acquisition system, a live position of the system can be measured, a real-time offset can be computed between the live position and a guide position (corresponding to a position from which a prior image of the subject was acquired at a prior acquisition time), and a guide can be overlaid on the viewfinder window to indicate a real-time positional offset between the live view and the prior image according to the real-time offset. A present image of the subject can be acquired when the guide indicates an in-time registration between the live view and the prior image.