The problem is usually due to graphics hardware
acceleration being used to display the image/video.

Newer media players normally use graphics hardware
acceleration on your system.

Graphics hardware performs a "hardware overlay" of
video on the screen, which bypasses the normal Windows
display memory that Snagit capture.

Most video capture programs that capture video from a
video camera use "hardware overlay" by default for their
video preview. This problem affects all screen capture
programs, and even the image put in the clipboard by the
Print Screen key.

The solution is to disable any hardware acceleration
in the application that is playing the video or disable
hardware acceleration system wide. Because this affects
all applications on the system, it may cause performance
problems for some applications and some applications may
not run at all.

How to disable graphics hardware acceleration globally for
all applications:

Windows XP or 2000: Right-click on the desktop and select
Properties > Settings > Advanced > Troubleshoot. Set the
Hardware acceleration slider to None.

On other versions of Windows: Select Control Panel > System >
Performance tab > Graphics > Advanced settings. Set the
Hardware acceleration slider to None.