To delete photos, you must be logged in.
Click the Tools Menu near the top of every gallery page and choose Delete.
The following will appear:

Simply click each photo you want to delete. They will be highlighted in red. Click Delete.
That's all there is to it.
Gotcha: Your photos are served up from many different servers for speedy viewing, and it may take a short time for deletion to fully propagate. Translation: Be patient. They'll make their exit soon!