I'm doing some testing on file uploads and discovered that the .bmp file format gets rejected even though defined in my config file as an allowed file extension.

I have added the following to my config file:

 'extraAllowedFileExtensions' => 'bmp, jpeg, tiff, pdf, cdr, gbr, gtl, dxf, dwg',
 'allowedFileExtensions' => 'bmp, jpeg, tiff, pdf, cdr, gbr, gtl, dxf, dwg',

This is the error I receive:

The file “/private/var/tmp/php7Md2bj” does not appear to be an image.

/shop/craft/app/etc/image/Image.php(138)

138    throw new Exception(Craft::t('The file “{path}” does not appear to be an image.', array('path' => $path)));

How do I fix this?