To take time-lapse photos, we set up a game camera looking over our shop. It takes pictures when it detects motion. Perhaps you can look into this..?
Also, I understand that pictures are a big part of documentation (I was our media and photography leader last year), but some times pictures can be inappropriate. I'm not saying that you shouldn't take pictures at all, but consider this; if you were using a machine that could severely hurt you, would you appreciate distractions such as a camera flash or the click of a shutter (I had an issue with this last year while I was running a lathe. The flash of a camera that was photographing me was slightly distracting). I'm not sure what kind of camera you are using or if your workshop is light enough to not use a flash, but keep these things in mind. I recommend getting a motion-detecting game camera (they are silent, and can even take some really funny pictures... That, and you can use them to capture safety hazards, such as students or mentors without safety glasses), or even using a smartphone with a high-resolution digital camera. Those are silent (if your shutter sound is off) and you have the option of not using a flash.
And if your students just have an issue with being photographed? They won't notice the game camera if you conceal it high on a shelf. That, and if you use a phone, think about it... What teenager isn't on their smartphone? It would look like you are sending a quick text or something along those lines. Or even checking Chief Delphi
