The image format used in a bootskin is simply a bitmap 'bmp', however it needs to be ONLY 4bit or in other words 16 colours.
The image, combined with the progress image and the ini file are then zipped together as your chosen boorskin name...ie. 'Myboot.zip'.
You then rename the extension to 'bootskin' as that is all the format is...a renamed zip and the result is a zip archive now called 'Myboot.bootskin'.
Simple as that...
