URL- and path-related problems are some of the easiest to diagnose and resolve because they tend to be binary in nature—they either work consistently or they fail consistently.
If image files (and other files) aren’t always displayed when you reference them from within ColdFusion, the problem might be path related. If you’re using relative paths (and you generally should be), be sure that the path being sent to the browser is valid. Having too many or too few periods and slashes in the path is a common problem.
Most browsers let you check image paths (constructing full URLs from relative paths in your code) by right-clicking (Windows) or Control-clicking (Mac) the image and viewing ...