Well there is your problem

, you can't use File when reading images from a jar file, you need to use an InputStream. File only works when reading files from a file system (as you are when running from eclipse).
Since you are using Slick you should use its useful ResourceLoader class to do this automatically for you (so doesn't matter if you are loading a file from a filesystem or a jar).
See the slick image loading tutorial
here.
So with your code you wouldn't use :
1
| basic = TextureLoader.getTexture("PNG",new FileInputStream(new File("res/tex/basic.png"))); |
but instead use
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| basic = TextureLoader.getTexture("PNG", ResourceLoader.getResourceAsStream("res/tex/basic.png")); |
As for your ImageIO.read line you can still use ResourceLoader as follows:
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| imageMain = ImageIO.read(ResourceLoader.getResourceAsStream("res/fonts/font.png")); |
hope that helps.