For the picture method to work the camera needs to be set as close to perpendicular to the frame as possible and then set at quite a distance and the zoom used to get well into the telephoto end of the zoom range. That'll flatten the perspective and make the tubes actually look straight. Something that won't happen at a wide or near wide angle setting. If this angle is off by much then the tubes won't be seen from dead on the side and the angles will alter based on the vanishing point lines. All in all you may find that you're getting numbers from the pictures but the picture may well not be as accurate as you think it is. Then there's our ability to judge the center of the tubes by eye to set the line over it at the correct angle. All in all by the time you introduce these sources of error you're just as well off with a hardware store angle guage or a cheap school protractor and a small plumb bob. The only truly accurate gizmo I'm seeing so far is the digital angle finder. Turn it on, zero it to the ground under the bike, assuming it's decently flat, and then take the angles of the tubes. Everything else mentioned here would do no better than + or - one degree. And the photo method could be way out depending on how well the camera is lined up to the bike and how well the bike is lined up to the camera. For example if you just lean the bike against a wall then the angles are going to be off by some amount. Unless that is compensated for by raising the camera so that it is a dead on 90 degrees in both axis then you may as well get one of the super cheap angle finders since it'll be easily as accurate or more so.