Which is a very good spot to give a warning.
Check your sources extremely carefully, even though the website may appear to be supplying very low cost or free stock images when they do not have the rights.
Getty images are undergoing a massive and wholly provocative campaign against site owners over the use of copyrighted images. Most of the site owners being targeted are completely unaware that they have an image that they shouldn't have.
One cited case is where someone used a cart image within and overall design and got clobbered for £1500. Another is where they used a picture of their own church on their site, unaware that the photographer had also listed it on Corbis - £3000.
Getty are kicking out thousands of these threatening and scary demands every week now and in most cases it is where people have obtained them through free or low cost sources.
In the past I have used what I considered to be reliable sources but so many people in the last few months have been hit with demands for well in excess of £1000 for an image worth about £2 that I will only use a trusted site.
As a web developer all I want is to have access to good graphics and images for which I am prepared to pay a reasonable commercial fee for. But Getty's tactics recently have left me and many like me cold. I genuinely do not feel I can trust Getty or related sites anymore.
I now refuse to to purchase from istockphoto, Corbis or getty (all owned by Getty). Fotolia seem to be genuine and I have written to them to get confirmation that they are providing properly authorised images and that they will not be pursuing the scorched earth policy that Getty do.
I totally agree that designers and photographers should be paid a rights fee and that copyright infringers should be stopped. But most of the targets that Getty are pursuing are first time offenders and most of them are innocent or unaware of any wrong doing. A simple, 'please remove it' or pay a small fine but not one in the 000's!
Be extremely careful where you source your imagery. It is your clients who will get a very big shock.