Qt-5.12.7 based.

The extension is .tgz but this is a normal .tar.gz archive. Extract with the usual command:
$tar -xvzf filename.tgz

The program is in the AppImage format: after decompress the archive, just give the executable
permissions to the Steg-1.1.0.0-x64.AppImage file:

chmod 755 Steg-1.1.0.0-x64.AppImage

And run it with ./Steg-1.1.0.0-x64.AppImage
Please take a look to the included README-linux64.txt.

If you like this software please consider to say "thank you" with a donation: