Thanks for your tree question.  You actually don't have a problem!  You have lichens living on your tree, and they will not injure the tree.  Lichens are an interesting symbiotic (living together and depending on each other) relationship between fungi and algae.  (The algae supply chlorophyll for the fungus; the fungus helps attach the two to the bark.)  Interestingly, you will not find lichens where there's polluted air!

Having said, that, there is some evidence to indicate that the lichen may be giving you information about the health of the tree.  I can see some apparently dead branches on the maple (which appears too large to be a Japanese maple from these pictures).  Here's a link from an Extension Agent in Delaware that explains these other issues.  Obviously, her suggestion that you bring samples to her office won't help, but you have an Extension Office in Baltimore; here's a link to its contact information.

Hope this is helpful.  Good luck!