Seeing it in action, I agree with Paulie D that it is actually 2 stills and the effect is probably applied by hand in some way. Given that it was filmed in 1977, there were no affordable computer tools like After Effects to use for a task like this. In fact, computers weren't widely used for doing this sort of work at that time.
While I can't say for sure the exact technique, I believe that they used a still image on which they traced a wide blue outline. They then probably used a chroma keyer to remove the blue and replace it with another signal. The other signal looks like colored noise which could be found by simply tuning a TV tuner to an unused channel.