A quick solution would be to use ones from openclipart. For instance, I could grey out and turn into a watermark the following images:
http://www.openclipart.org/detail/4749
http://www.openclipart.org/detail/1646
They would be small and grey and not show much detail so imperfections would not be apparent. I can do this on Monday.
However, I think that good photos for as many team members as possible would be an asset. Matthias for instance has a professional and welcoming image on:
http://test.fsfe.org/about/kirschner/kirschner.en.html
Sam.