I use Black Glass Enhanced (curiouso9.deviantart.com/art/Black-Glass-Enhanced-v0-5-156752713) with my black Windows 7 theme. Unfortunately, Windows Photo Viewer does not have any transparency like all my other specified programs. When Windows Photo Viewer executes, it runs as dllhost.exe, which is already on the list of programs to make transparent within Black Glass Enhanced. So I'm not sure why it isn't "glassifying" properly.
The first screenshot is Windows Photo Viewer; and the second is Windows 7 Gif Viewer (www.sevenforums.com/music-pictures-video/97830-windows-7-gif-viewer-works-perfectly.html), which is just Windows XP Photo Viewer transferred to Win7. Windows 7 Gif Viewer executes within rundll32.exe, which is also included in the list on Black Glass Enhanced. And as you can see, it is properly glassy.
I tried this method (superuser.com/questions/719867/how-to-change-the-background-color-in-windows-photo-viewer) to change the Photo Viewer background color manually, but changing it had no effect on transparency. Is there a DWORD value that can achieve this? Or remove the background block entirely and make it look like the Windows XP Photo Viewer?
P.S. Sorry for the long links, it wouldn't let me post hyperlinks.