LoremFlickr provides placeholder images for every case, web or print, on almost any subject, in any size. It's simple and free. Just put the custom url in your code like so:
<img src="http://loremflickr.com/320/240" />
A random picture of 320 x 240 pixels. If not supplying any keyword, you'll get a picture matching the keyword kitten.
A random picture matching the keyword dog, of 320 x 240 pixels.
A random picture in gray matching the keyword paris, of 320 x 240 pixels. Besides g, you can try p, red, green and blue.
A random picture matching the keywords brazil or rio, of 320 x 240 pixels.
A random picture matching the keywords paris and girl, of 320 x 240 pixels.
A random picture in grey matching the keywords paris and girl, of 320 x 240 pixels.
If no matching photos are found, a photo of Machu Picchu is returned.
Your browser might cache the images when you request the same URL multiple times on the same page. You can resolve this by adding a meaningless querystring to the URL. So, for example...
<img src="http://loremflickr.com/320/240?random=1" /> <img src="http://loremflickr.com/320/240?random=2" /> <img src="http://loremflickr.com/320/240?random=3" />
Yes, at least until the bandwidth usage spirals out of control, this service is free. But, feel free to donate.PayPal.Me
If you want a daily image on your favourite collection of keywords, here's an example of an RSS feed that will deliver a fresh photo to your RSS reader each day.
The d parameter for periodic updates is currently the only one that's supported.