Are "celebrity" portraits from photos valid?

[David Dowbyhuz]

Thanks for the input. It's sure what I'm asking for.

I fully appreciate the tradition of painting from life, and know the limitations placed on purely photo-sourced work, but I'm sure I'm not alone in the circumstances of struggling to make time to paint. I could not give fair attention to a live model, and no model would put up with my erratic schedule.

I'm sure my evolution as an artist will be the poorer for the lack!