Damaged wood in my shower. Is it mold?

Hi all,

I am visiting my parents for a couple weeks and I noticed that the wood in their shower window is deteriorating and rotting. I called a local business and they said it would be $150 to come do an in-home assessment. I figured I'd come here for a quick sanity check. If this is just dirt and rotten wood, then I'll do the repair myself (rip the siding off, clean up the insides, replace the wood and seal it, etc). But if it's mold, then I'd rather have a professional service take care of it. I don't want my parents living in a house with mold issues.

So anyway, please take a look at my little album here which contains pictures of the situation. I can take more pictures upon request if these are not adequate. Thanks in advance!!

https://drive.google.com/folderview?id=0By4MbtYQ4L-jSVBmRmhSZzhnd2s