The basis of this is to take tons of high quality photos and upload them to Flickr and other image sharing sites. Set the rights to Creative Commons. In the description, ask for them to use your website link as a source when they use the image. This is a long term, white hat strategy. I've given many DA60-80 backlinks to these photographers in my articles when I use their images. I probably ramble too much, but I hope it will help a few of you. Enjoy!