Ahh, likely a common mistake.  There are two primary causes of this problem.

1) Pictures are displayed in a web page by using a reference within the code telling the web browser where that picture "lives".  The problem may be that these references are wrong.  Often when the site is built on your personal PC and you create references to pictures you create references to the pictures in various folders around your PC. 
To see if this is the problem, open your web page in your web browser (Internet Explorer, Netscape Navigator or whatever you use).  Hover your mouse pointer over one of the red X's and right click.  Choose properties from the menu that appears.