I used Photoshop's image distortion, skew and perspective features
extensively to "fix" many of the photos on the site so that it looks like
the camera was centered in front of the center of the dial faces.
Keep in mind that the gnomon in the processed picture will be "funny". If you only use the hour lines to calculate the latitude you will be OK. I think it should also be possible to determine the latitude from the gnomon without reference to the hour lines. You will still need to use clues about the vertical and horizontal, and you will need both the free edge of the gnomon and the line where it intersects the plate, plus the assumption that it is perpendicular to the plate.
--Art Carlson
