A Windows bitmap image (.bmp) is not the same as a Windows icon (.ico).
The .ico file format contains several images and while the individual images may be stored in roughly the same way as a .bmp file, there is an important header at the beginning of the .ico file, which is missing in a .bmp file.
It is a widespread myth that it is possible to safely rename .bmp files to .ico files, but it is not true. While it may occasionally work, this is purely a coincidence. Applications, which are able to read both .ico files and .bmp files, will sometimes ignore the extension and use the file despite the wrong extension (Firefox is a typical example).
Particularly web masters trying to create a favicon for their web site are prone to take this shortcut and then wonder why isn't their favicon.ico working in Internet Explorer.
To convert .bmp to .ico, use a dedicated tool:
Anonymous
on March 8th 2016
i changed out the ext name from the dot(.) rename .bmp to .ico the dot(.) must be changed as well in all windows from Xp to win 8 win is different first you need to find how to un-hide the file extension first which i am still looking for
Anonymous
on August 22nd 2020
To view the file extensions in Windows 10 File Explorer, click on the 'View' tab. Then all the way to the right click on 'Options' > 'Change Folder and Search Options'. Once more click on the 'View' tab (of the popup this time). Go down the list of 'Advanced Settings' until you find 'Hide extensions for known file types' and Uncheck it. .dt
Anonymous
