After indexing the image, put it in your Graal folder and delete the file FILENAMECACHE.txt from the Graal folder. FILENAMECACHE.txt is a list of files cached(stored) by Graal. It tells Graal exactly where to find images, so it doesn't have to scan the whole Graal folder every time Graal starts up. Graal's tools also rely on this. If you just drop an image into the folder, Graal never finds it, thus never even knows it's there. Deleting FILENAMECACHE will force Graal to rescan the folder, thus finding your newly added image
Alternatively, you can put the image in the same folder as the gani itself, and open up the gani directly(by associating the file type with Graalshop). This will make Graal temporarily cache the whole folder that the gani is found in, meaning it will also find your image. This can only be done if you the images are found in the same folder as the gani. However, I suggest the above method.
Also, this is what your indexed window should look like:
