Level 11Whenever you have a username/password combination, you will always get them at the same time, with the exception of level 13. So be aware of that for this level. Not much can be said for this one, just look for unusual and out of place things in this. The creator never tries to trick you on what page you are on. So be aware of what things look like in relation to one another.
Level 12The picture and the caption below it (plus hints in the source code and password field) are all you need to solve this one, but for people who aren't good at doing the "trick" required here, there's luckily an alternative way to solve it.
It's worth pointing out that the "dragon.zip" link at the bottom of the source does link to something interesting, but it's not needed for the puzzle and doesn't provide any hints towards it. Sometimes the best way to give a hint towards a level is to say what isn't important, so it's good to rule out things like that.
Ever look at one of those "spot the differences" puzzles? They were popular in kids' magazines like Highlights for Children. This puzzle is similar to that, but the images shown here are from slightly different angles, just keep that in mind when you are trying to figure out what's different.
Level 13This level has a fair amount of information and it can be hard to know where to start. Just write down all the things you think may be useful in that notepad I know you're keeping. This is the level where you get the username and password separately, but of course it's still on the same level, just not in the same image. You can extrapolate the password from the other word you found in this level. Who is the "I" referring to in one of the hints?
Also, since I remember personally having trouble with this one when I first started the puzzle, you may want to keep an open mind when it comes to some of the shapes in the image. Not everything is necessarily oriented right-side-up.