You should read the thread before you write something, fenlander. He already mentioned that he is on a JFRV. He works 2hrs/week for that school.
I don't see the big deal, personally. Your employer(s) would know that you are free to work anywhere with this type of visa. It's a chance they take when they hire you. They should know that your picture could end up on the brochure of a competitor. However, Marty did ask for his pictures not to be used outside of the school. I would be ticked, too.
With only 2 hrs/week, you have little to lose, Marty. The legal route to go about this would be to write them a letter and have it mailed to them via registered mail. Mention in the letter that you refuse to have your picture used without authorization and failure to comply to your request you will initiate legal proceedings. Instead of using registered mail, you could hire a lawyer to send in the request, but the lawyer would also use registered mail. You can skip legal fees and send the registered letter yourself.
You can also choose to sue immediately if they already distributed some of the brochures but I think that would be overly vindictive and unnecessary. See if they will comply to your original requirements first and understand that you are most than likely to lose two hours of work per week in the process. They will not want you working for them after that. Moreover, if you sue them, they are likely to find something to sue you for even if they have to lie. Do not underestimate the consequences of making people lose face in Taiwan. It's so not worth it for you to sue them over this, but a simple threat, in writing, might be enough to get the brochures out of circulation.