Thank you for allowing me to assist with your question.
You may use Pixabay.com, Clker.com, Morguefile.com images without attribution for commercial purposes, as long as that purpose is legal, and not used in a "derogatory" way such as hate, pornography, etc.
I've read the terms at each of these websites, (and I have used them myself in some of my own web work.)
Thank you for joining me. If you have further questions about any of those terms, or how you intend to use them, please feel free to ask.
My goal is that you feel you have received Excellent service. Warmly, Pam Heslin
Ok, so it appears that they do have sweeping statements, unlike www.sxc.hu, which includes many photos that actually do require attribution, even though you may still use such a photo commercially. Thanks.