First launched in 1999 and brought into the mainstream by 7-zip compressor, 7z files are those which contain compressed data, which may need to be extracted before it can be accessed.

To open an IMG file and view the contents in Windows 7, you need a third-party file extraction program such as WinRar or 7-Zip.

7-Zip is an Open Source File Compression & Archiver software for Windows 11/10 PC 64-bit too. Read review & download it free. Portable version available.