A portal with links to websites for good quality images with CC license for unrestricted use.
NB You should always verify that the work is actually under a CC license by following the link.
What is Creative Commons and how do the licenses work?
Creative Commons (CC) is a way of licensing material to protect some of the rights, rather than copyright which protects the work entirely. You can find out more about the Creative Commons movement and the licenses on the CC website.
So, for example, some people are happy to allow you to re-use their work (e.g. an image, a video) if it's for a non-commercial purpose and if you give them credit.