Be Very Careful:
* Where you get your images, imagery is frequently stolen and then purported to be "public domain" or "free use".  Before purchasing a license, always read the fine print in the end user agreement. Beware when it says something like:
"You understand that these images are copyrighted and may be owned by a third party, and any unauthorized use by you may be an infringement of such copyright." or "You acknowledge that we have not made any representation that your use of these animations will not infringe or violate the trademark rights of any third party..." or "You indemnify us from any and all claims, damages..., including attorneys' fees and expenses, arising in connection with your use of the content on this site..."
* Animations should not contain elements of copyrighted or trademarked works - For example, using an image of Mickey Mouse or Homer Simpson or .... and animating it is a copyright infringement.

Respect Copyrights:
* Putting an artist's animation or graphic on any website or collection page - unless your sure it's free and not copyrighted, can be costly to the artist and an infringement of use or distribution rights. (Many artists sell their distribution rights and if their art is being distributed for free they loose income...)
If you're unsure, read the information in the file itself *. Read the license agreement that comes with your software and find the original owner/artist. Most artists will tell you somewhere on their web pages what the terms of usage are, so read carefully. 
* To check on authoring information within an animation, download an animation program, such as Ulead's Gif Animator, open the animation and read the comment file. If there is no information available, it doesn't necessarily mean the animation is shareware - because this info can be removed by optimization programs. Most often you will find an artist's name who you can contact for copyright and credit information. 

* Changing a graphic without permission. Many people think that by modifying the original they are safe or that it's ok to make small changes. Coca Cola and other household names have proven this to be incorrect. It is an infringement of the copyright. If you want to modify art in any way seek the artists permission. Ask him/her to approve your modification.  Even small changes like removing backgrounds, adding your name... If the artist denies you approval don't take it personally. It can make it more difficult for the artist to pursue their own copyright claim if he/she gives permission and then modified work has been stolen. 

How to Link: Download!
* Do not link directly to a graphic. Don't include anyone else's URL in the BODY BACKGROUND or IMG SRC tags. This can cost the artist a lot of money which could result in their web site being shut down. 
If you don't know how to save or set up an image on your Home Page, ask the person whose page it is on. You will find they are as generous with help as they are in providing these graphics.

Commercial Use:

* The net is so wonderful and one reason for this is free graphics. Do not use copyrighted images without permission in a business/commercial site. Most graphics are for "free" use only on personal sites. 
For clarification, a website is considered by the copyright holder to be a commercial website if banner space is sold on a personal website. If a person makes any money off of any portion of their website, regardless of how much or how little, then it's a commercial site. A website is considered to be a commercial site if it's owned and operated in conjunction with a revenue generating site, regardless of whether the owning entity does not make money off of the portion of the website where the content is shown. An example of this would be an e-card site delivered free of charge by a commercial entity, or similar free attraction used to lure visitors to the revenue generating portion of the commercial website. Non-profit organizations or charities are considered by the copyright holder to be commercial entities. If you are a webmaster in the business of creating home pages or if you own a business and are promoting it on your site, you are considered commercial. 
Write to the owner of the graphic and send your URL to seek permission. Perhaps you will be able to buy or use the graphic. If you are making money with the image, so should the artist. 

* Re-selling images. Some people try to make money with free graphics. It's tempting to download graphics and start selling them. We all can stop this kind of business if we don't buy it.
 

Artists: Stay informed. You have a right to protect your work,  media laws change and their are restrictions on what you can ask for and rules on how to go about doing things.  When you write a request asking your work be removed from a site - cool off first and be as nice as possible - there are a lot of innocents out there.
Freelance artist, you will be presented with some pretty scary licensing agreements and contracts.  Read them well, get help if you don't understand them, ask for changes if needed.