I know they both mean the same thing, however I am just not sure if when writing, one should be used over the other depending on the context?

Well, firstly 照片 is a photograph, from a camera. It's probably most commonly used.

As for 相片, my Chinese dictionary says "Now the norm is to write '像片'", and under the definition of 像片 it says "人的照片". A photo of a person.

I'm not sure if the dictionary's right here, but that's one angle.

Makes sense. 像片 refers to a photo of a person.

I really need to get myself a good chinese-chinese dictionary.

Thanks!