Feedback+edits for Image Processing chapter

@golanlevin I'm helping out with a class that is reading your book chapter this week, so I took a pass at it with some small edits.  Inline comments are in **[MH: comment]** format.

It's a fantastic chapter so far - clear and easy to follow!  (Great Lincoln graphics btw.)  I look forward to seeing the rest of it filled out.  It looks like you've got a ton planned, so I'm wondering if maybe this chapter needs an abridged version (foundational concepts + bare bones version of blob and face tracking scenarios + links to where to go for advanced considerations) and an unabridged version.