The IT people didn't bother making the image that was displayed on the log in screen read only.

Later we found a way to get all the teachers usernames, so we used the school's website to brute force accounts. 17 out of 70 teachers used "password", "123456" or "qwerty" as their password. Using a teacher account to remote control other student's PCs was inevitable. Later, I found that a test account with basic admin powers also had "password" for a password. Unlimited printer credits and banning people I didn't like at will was most enjoyable.