Journalists, bloggers, and designers will find desktop search engine CCFinder (free for basic service, £10 for Plus version) handy because it makes finding legally reusable images on the Internet quick and easy. Photographers can attach one of several different Creative Commons licences to their images to let online viewers know it is okay to reuse them, and in what way. The CCFinder software aims to take the sting out of the work of finding such images. See all software downloads.
The rub with this software is that once you click on a picture in CCFinder, you will immediately see the limitations. You can download the photo to your computer for no charge, but colour filters and PDF downloading are disabled by default until you pay a "donation" of £10. If you like the software and use it a lot, you may decide upgrading to the Plus model makes sense.
Operating CCFinder isn't a problem. Just enter your search term (as you would with any other search engine), choose which filter you want and press "go." The images that match your search term and filter will then be presented and you can click on one to see it in a much larger size.
On the larger image screen, you are presented with the various terms and conditions for that image so you don't run afoul of the photographer's wishes and misuse the image. You are told if you need to attribute the image to the photographer or not, under what circumstances the image can be used (commercial or non-commercial), and whether or not you can alter the photo in any way.