New to Java

Hi

I'm trying to find out why my jar file won't work. My program compiles and works ok when launched from BlueJ. It is a game and it makes use a several images. If I compress it to create a jar (including all the used libraries, the source code and selecting the class with the main method) and then i click on the file nothing happens. If I execute it from the command line a get a long series of strings going:

java.io.FileNotFoundException: Cannot read image file "images/walk-left.gif"

And there's basically one of these lines for pretty much every image used. This screen closes up after like 1 second.

My pc runs jar files ok as I tried others..and all the images are inside the jar file in the same directory where they should be...I'm really confused.

Any ideas what this could mean? Is there a special step I've missed when it comes to creating .jar files of codes that access files?

Thank you very much for your help