2. You will annoy some visitors who are right-clicking for other reasons such as to bookmark a page, reload, go back, or to use any plugins or other special web tools they may have set up.
The end result then is that you needlessly aggravate innocent users without doing anything to deter image-swipers. Frankly, it's a losing strategy that alienates the viewers you want to keep around, and has no impact on those who want to use your images.
A far more effective approach is to apply a watermark to the image prior to uploading it so that even if the image is saved or captured, your school's copyright appears. Picmarkr is a simple, free tool that allows you to upload images from your Desktop, Flickr, Picasa, or Facebook, add custom text or image as a watermark, and download back to your computer (or back to Flickr, Picasa, or Facebook). You can use this tool to easily add a non-removable watermark to your image, rendering it useless for anybody else to lift and pass off as their own image.