I was just adding a single image to a GWT 2.4 application I was working on. I just put it under the images folder in the war and I had it working properly until I would compile it. Then it would get deleted from the folder. If I remember correctly, from working with older versions of GWT, you could just put an image in this folder to use it.
It just took a few minutes to convert the code to use an ImageResource, but do you have to use an ImageResource for just one image or is there another way to do this?
The class ImageBundle is deprecated, try to use ClientBundle instead.
Instead of putting the file in the war folder, which is typically generated, try putting it in a folder called public/ in the same directory as your client package. The compiler will move it then into your module directory.
And finally, ClientBundle (and ImageBundle, but don't use it) will automatically try to sprite your images where possible, and in some cases include the image in your main html download so that the user only needs to download and cache one large file instead of several files - even for individual images it can be worth it for repeat users of the page, to ensure that no caching issues ever occur.