Some notes:
When running "voidimageviewer.exe /gif", voidImageViewer will attempt to relaunch with administrative privileges.
I've check this on Windows 8.1 x86 / Windows 10 x64 and it appears to work:
When I run "voidimageviewer.exe /gif" I receive a user account control prompt to allow voidimageviewer to make changes to the system.
When I open a gif file I receive another notification at the top right of the screen that new apps that can open this type of file.
If I click on this notification, I can choose to click on voidImageViewer, which will then open my gif file with voidImageViewer.
What are your User Account Control settings (under Action Center)? -Perhaps voidImageViewer is blocked?
Do you receive the UAC prompt when running "voidimageviewer.exe /gif" ?
Does "voidimageviewer.exe /gif" work from a console run as administrator?