Over at Wizards of the Coast, on their D&D site, they have a fan site kit available for use. I found it a few weeks ago as I am doing the same, as far as putting together a homebrew website. Along with images they have the D&D logo and clear instruction on the use and protocol for the free images, giving you everything you need to stay well within the legal boundaries of the copyright issues :
Use Trademark and Copyright Notices. All Fan Sites must include the correct copyright and trademark information on each page that contains content related to Wizards' property. When referencing specific game names, game terms, or characters, the appropriate TM or ® should be used as provided in the relevant Tool Kit. For example,"Wizards of the Coast, Dungeons & Dragons, and their logos are trademarks of Wizards of the Coast LLC in the United States and other countries. © 2015 Wizards. All Rights Reserved."Further, on every page of a Fan Site where Wizards Materials appear, you must include the following notice in a font legible to end users of the Fan Site: "This [Web site] is not affiliated with, endorsed, sponsored, or specifically approved by Wizards of the Coast LLC. This [Web site] may use the trademarks and other intellectual property of Wizards of the Coast LLC, which is permitted under Wizards' Fan Site Policy [link]. For example, Dungeons & Dragons® is a trademark[s] of Wizards of the Coast. For more information about Wizards of the Coast or any of Wizards' trademarks or other intellectual property, please visit their website at (www.wizards.com)."
Here is a link to the page, where they break down the usage rights and other info pertaining to the kit. A lot of good stuff. http://dnd.wizards.com/articles/features/fan-site-kit
Another good place to peruse is the DungeonMasters Guild http://www.dmsguild.com/
Great place to find fan made products ranging from art to new game mechanics (new races, classes etc) and adventures. The site is set up for people to be able to sell their D&D related creations, and everything there is reasonably priced (aka cheap), pay what you want, or a decent amount of stuff is free. I've found a lot of great material there as well.