Automatic Placeholder Images from Flickr
flickholdr.com
flickholdr.com
It seems to me that embedding an image on another site, even with a copyright notice, would be reproducing the image and not allowed under the normal terms of a copyright license.
Sorry to be a party pooper, but just ignoring legal issues around reproducing other people's content (some of whom make a living from selling it) isn't going to make it go away.
Edit: to answer my own question, the images are only Creative Commons attribution-licensed photos. From the 'about' page:
> The photos are pulled from flickr using its search api, searching only creative commons material, and watermarking them with the name of the author, to be in accordance with the creative commons licences, which all require attribution
Nothing R rated or tasteless, just not the kind of thing I want to explain to my boss who's looking over my shoulder. Think I'll be sticking with http://placekitten.com/ then...
Try and be a bit more specific in your tags, putting several separated by commas.
http://flickholdr.com/250/185/happy,office for example, might be more appropriate.
Disclaimer: I'm the developper behind flickholdr