The only usage preference I'm aware of is that artefact is preferred in British English and artifact is preferred in US English, but that both are acceptable in either case.

See Oxford Dictionary, for example: http://oxforddictionaries.com/definition/artefact

Personally, I tend to mix them the same way you do - I collect artifacts in Tomb Raider and my compressed photos have artefacts!

The only usage preference I'm aware of is that artefact is preferred in British English and artifact is preferred in US English, but that both are acceptable in either case.

See the Oxford Dictionary, for example.

Personally, I tend to mix them the same way you do: I collect artifacts in Tomb Raider and my compressed photos have artefacts!