This came out of code review in the ImageStorage class:

    byte[] header = new byte[getMaxSignatureLength()];
    try {
        ImageTools.readFully(stream, header);
    } catch (EOFException ignored) {
        return null;
    }

This code will take the largest possible signature length for known registered types (ie. JPG, GIF, BMP, PNG) and load those bytes. But if one of these formats could store a tiny image that would be smaller than the largest signature, then that image can't be loaded as this code would throw EOF and not return a suitable loader...