Images Flashed On My Screen -- Attempted Subliminal Programming?

Last night while surfing this forum, an image flashed quickly on the screen. Note that I was simply reading a thread in the forum; nothing special.

It's not the first time it's happened, either. Images have flashed before my eyes a few times while reading this very forum.

Have any of you noticed the same and can I record my online activities so that I can stop it frame-by-frame to see what the image actually was?

Thanks for your help.