Ask HN: What's the best (crowdsourced) content filtering service?

I'm working on an educational project which involves users taking photos and uploading to our servers. They can then browse the site, looking at other photos. Since we anticipate people of all ages using our site, we need to filter the images for offensive or off-topic images.

What's the best service to use for this? We need there to be an API, and using crowd-sourcing rather than automatic algorithms (because of higher accuracy).

I'm looking at crowdsifter.com and socialmod.com but have no idea which is better or if there are other better options. Does anyone have any experience with these or other similar services? I'd prefer not having to write an mturk tool myself...