I was curious so I went to PhotoBox and read through their material.  I then emailed them saying I was an artist and might be interested in uploading some art material for greeting cards.  I asked them a couple of technical questions about their uploading procedure and artists rights.  I received an email -- undoubtedly a stock reply form that had nothing to do with my questions.   I emailed them back asking why they had not answered my questions and I never heard back from them.   They may be reputable but they don't present a good picture.