What are the permissions of your Pictures directory? If you want to use symlinks, than the folders and files that you link to must have permissions that allow Apache to serve them. By default, the Pictures directory has "600" permissions, which only allow the user to read and write. If you want Apache to serve from that folder, you need to give it "755" permissions, which can be done with "chmod 755 /Users/marty/Pictures/". Using a similar configuration as yours, fixing the permissions was the clincher to get things working on my end.
Your PHP program problem is a fact of life - some programs, either by fault of the language or the developer, don't understand symlinks, and will show them as a file, as you've been seeing. I'm not sure how PHP handles symlinks, but I'm sure you can Google a bit for the answer.