Launch Microsoft Paint. Click "File" followed by "Open" from the main menu. Find and open the image that you want to use as your Blogger button with Paint's folder and file browser.

If you want to open & view ITHMB files on Windows 11/10, ... You will see four buttons: Open, Convert, Print, ... JPG, or any other format and then use some image viewer to open the converted file.

If your PC doesn’t have the PrtSc button, instead press Fn + Windows key + Spacebar. To locate the image, open File Explorer, and go to the Pictures folder and then the Screenshots subfolder.