Amtul asked how to measure angles on a digital photo of light reflecting off a curved mirror, here's how to do it in GeoGebra.

First I insert the image (a screen shot from Algodoo). Then make it the background (right click object properties). Then I made a circle and adjusted it so that it gave the centre of curvature. A line was placed to act as a normal. The angles can then be measured with angle tool.

Good luck.