Many schools have their own sites. For example, the school I used to teach at has a site (including a photo gallery) set up by an ex-pupil. Inspired by this, I put another site online which has nearly 500 photographs of past pupils. (I can't see much point posting the links here but you're welcome to them if you want them).
Try a web search for the name(s) of your old school(s). You might suddenly find that you're looking at a picture of yourself! (Hopefully, not too embarrassing!).
Chris