Whenever I add files (image, mostly png) with an initial letter of i or "bigger", they dont show up in the applicationController/ressources/images/... directory in the Application Navigator.
Folders don't show up at all, and if there is a folder with a smaller letter than any image file, then all the following image files aren't shown.
Pascal, what is your intent here? Are you going to use these images in a springboard or some other content? If so, they would go under the public_html folder on your drive which is visualized in JDev as your "Web Content" folder. If you place files or folders under the ApplicationController/src folder, they will show up under "Application Sources" in JDev.
If you really want to include a specific folder as a resource, you can go to the project properties of the ApplicationController project, select "Project Source Paths", expand it and select "Resources". Then in the bottom section you can add a folder and it will then be included in your "Resources" of your ApplicationController project. I'm still not sure this is actually what you want though.
I should note as well, I did not see or reproduce the problem you are seeing with filenames > H. Could you post exactly what you have in your directory structure on disk as well as what you see in JDev.