Mammatus clouds over Saskatchewan. Source
This strange image may look like there's something wrong with the camera, but what you're seeing is an actual phenomenon. The bright blotches in the sky come from light reflected by bumps in these mammatus clouds. Normally the bottoms of clouds are flat because of the way they form. Water vapor begins to condense at a very specific temperature that usually corresponds to a very specific altitude. These mammatus clouds, however, have very large and obvious bumps hanging down. Why is this? The easy answer is that we don't really know. There are a lot of theories involving anything from convective currents to ice particles falling. Regardless, they are fascinating to look at.