The interjecting of random pictures leaning on a sexual nature is not allowed. For one simple reason:
People browse this site from work. Someone maybe scrolling through a harmless thread here about anything and someone decided to post a picture of a half-dressed woman or .gif of a cartoon woman with breast bouncing up and down. Just at that moment a female co-worker,HR director, or the boss walks by and looks at the screen.
How do we know? There have been threads in the past of people being written up at work and I remember on one being terminated.
Don't do it.