Flickr hosts millions of images that are licensed under a Creative Commons license or are in the public domain (Flickr Commons). Depending on the license, you may use the images on your private or commercial webpage, or can make changes to it.
If you want to use these images, you need to to the following:
With ImageCodr.org, there is no need to do all this manually, you simply enter in the URL of the picture page (as seen in your browser) you are interested in and ImageCodr.org will generate the ready to use HTML code. It will also display a brief and easy license summary, so you don't get in legal trouble because you missed something.