Old cameras can be part-exchanged at photographic shops, second-hand shops or sold on sites such as E-Bay.

If you use a so-called disposable camera then make sure when you take it for processing that the processor guarantees to recycle the camera. Some companies, like Kodak, have good records on recycling their disposables. If you drop off a camera in a Kodak booth the camera is pretty much fully recycled, including the battery.

Avoid "reloaded" cameras. These have new films put into old bodies, but quality is frequently a problem due to the conditions in which the new film is loaded.

And in general - avoid using disposable cameras if you possibly can!