Many websites offer free wolf images with a watermark on the photo or drawing, but there are also sites that offer full-sized, watermark-free images that cost no money to download and are free to publish or reproduce as long as credit is given to the photographer or artist. Three such sites are Wikimedia Commons, morgueFile and Flickr, though use of some images from all three sites is restricted.
Flickr's search engine turned up more than 1.4 million results for the term "wolf" as of September 2015. Some of these images are categorized as "All Rights Reserved," which means they can't be reproduced publicly. Others, including those tagged "Some Rights Reserved," may be copied and distributed in any format or medium.
On Wikimedia, a search for the term "wolf" turns up many photos of wolves and wolf subspecies, categorized in sections of various parts of the world. The search terms "wolves" results in several categories appearing, including wolf tracks, wolf behavior, people with wolves and wolves in art, which has many sub-categories.
The morgueFile search engine includes an option to search for free photos. Searching for "wolf" under the free photo designation results in 103 photos and a search for "wolves" results in 48..
Before using any image, check the information associated with the photo on the website to see if the photographer or artist allows reproduction. The mechanisms for downloading images vary from site to site, but often a right click on the image works. At Flickr, a small arrow on the bottom right of a photo's Web page enables downloading when clicked.