I used to upload bmp just two days ago. They appear as whole images on the screen, jpg as small. Anyway jpg is smaller file, so I guess I will use this. I did not know that some browsers would not show bmp.
I tried with another browser and it is the same, but I found that the actual problem is that it cannot upload bmp and tif files. What appears on the screen is a dot. It can upload jpg, png, gif.
Yes, I went through that and did the following.
Deactivate plugins, swich to twenty thirteen theme, the problem remains.
Upgrade WordPress 3.7 manually, through copying files from the zip file. The problem remains.