I don't think the primary effect was for the "image" to be funny but rather to fool people into thinking (click click click click) why isn't this video working?. Though there are may obvious reasons upon hovering over the image (as well as the title) that gives the whole "January's fool" posting away without even making a click .
Obvious to some, less obvious to others. Apply a poll perhaps? How many clicks did you make before realising it was an image?