According to the docs[1], `progression` is the info property when opening a jpeg, and `progressive` is the parameter when saving. If I print the contents of the img.info from a jpg created in Photoshop, both `progressive` and `progression` are there. I assume there has been confusion in the past and image editors throw them both in to be sure.

Feel free to merge, and thanks for your help!

[1] http://www.pythonware.com/library/pil/handbook/format-jpeg.htm