Hi Gem!
It is because ImageGlass installer was not signed!
So the smart screen of Windows recognizes as Unknown Publisher, and it throws a warning popup.
You can just click on More info link to reveal Run anyway button.
I am trying to buy a code signing certificate for the next versions.
If you really care about the security of the file you downloaded, you can check the hashed code of your downloaded file, and compare to the ones provided on ImageGlass website (SHA1 Checksum):
https://imageglass.org/download
If it doesn't match, your file might be not original, or modified.
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Phap Dieu DuongAuthor of ImageGlass software
[Skype] d2phap