JPEG (JPG) is most efficient image format and is preferred format for uploading and displaying images on the internet irrespective of publishing platform. Due to its small size, it consumes less server resources and loads much quickly for users. BMP image format is exactly opposite with huge image file size. Due to this, you may want to disable uploading of images in BMP format on WordPress website or just allow JPEG image format uploads.
Disable BMP & allow JPG, GIF, PNG image uploads
Restrict Uploads plugin automatically enable JPG, GIF and PNG image format uploads on WordPress website. It disables every other file type uploads including BMP images.
If you attempt to upload file type other than JPG, GIF or PNG, then you should see: “Sorry, this file type is not permitted for security reasons” error in the media upload window. Even though this plugin look out-dated, it should work fine (tested in WordPress 3.6).
Allow JPG & disable uploads of other file formats
Allow Only Jpegs plugin is a blessing for an image intensive blog with multiple users. It restrict users from uploading images in heavy formats like BMP. Once you activate this plugin, users can only upload images in JPG (JPEG) format. To tighten image optimization further, you can install WP Smush it plugin to auto optimize JPG images during upload process.
Both plugins work great in the background. You can tweak file format type permissions by editing plugin code (suggestion for PHP geeks!). As such there are no settings for either plugin, just install and activate for it to work.