There are thousands of free background images available on the Web, but only a small percentage are acceptable for use on professional quality Web sites. They cut themselves on broken code. Even simple HTML code errors cause serious problems. Visitors may be treated to some bizarre font and color combinations if your code contains improperly nested tags . It often depends on how the browser chooses to interpret the code.
Browsers are picky.
They want the tags used properly before they'll accurately display your Web page. Of course, wading through pages of HTML code looking for errors may take more time and expertise than you posses. If so, use an HTML validation tool like HTML Toolbox. It looks like an old science experiment. Ok, so maybe you have updated your content since the year 1215, but you'd be surprised at how outdated some of the stuff on the Web really is.