Checking individual pages is free.
Commercial licences are available for checking organizational web sites.
NetMind Free Services Home Page - URL Minder will notify you by email when any portion of a web page is changed. These are all free. Most of the basic html sites cover design issues as well, get the basics first. The best way to find clipar t fast is to use a search engine with the keywords clipart and the name of the image. The section on using and making images is very helpful.