Continuing the discussion from LaserWeb Freezes on larger BMP files:
Discourse will not render BMP files inline, I believe. However, I have added bmp as an enabled extension because some of the communities share BMP files. This is expected to not display them inline but at least let you download them.
If you need to share a BMP file on this site, you should now be able to, but if you want an image to display in your post, convert the BMP to a PNG file please (and thank you).