ski photography???? I recommend taking a real elements of photography and analyse that. Some examples would be line, lighting, depth of field, texture, compostition, etc.
OR
take a field of photography such as landscape, street, portrait, Macro.
Another topic i have done is a comparision of B&w film vs Color and how each element(light, line, texture, compostition, exposure) is affected by it.
Or
If you like action shots, write an essay on the different approachs to capturing motion. The idea being to explain how changing the ISO speed, F/stop, Depth of field, Exposure, lens, lighting and angle can create a very different mood. You would probably want to be able to shoot some examples though.