Hi friends @amritadeva! I have been pondering this exact question myself, not explicitly about thumbnails but in the general guise of how to get people to click and read. This from another friend of mine who is very successful at online ad campaigns and if it works for ads it should work for thumbnails:
The image's number one job is to grab people's attention and pull their eye to the headline. To do this effectively, the image must function as a pattern interrupt.
That's why nice shiny stock images almost never work: they just blend right in.
The key is to pick bright, unusual, or strangely-cropped images that leap off the page and catch the eye.
But that's only half the equation.
Being eye-catching alone isn't enough. The image must also have a "loose connection" to the offer.
In other words, you want the image to be relevant to the headline and offer... but not TOO relevant.
You want there to be just enough dissonance that the viewer has to stop and try to figure out what the connection is.
His website is thirdwayman.com, he usually focuses on helping find what drives our passions and getting moving, but is also giving pointers on how to establish and grow online businesses.
Anyway, I agree with your intuitive premise that print and video venues need different thumbnails, their user bases are different...as well as the size issue. If you figure it out share because I am confused too! Your backgrounds and thumbnails are really nice:-)
Cool, thanks, that is really valuable info!! And also makes a lot of sense, the way your friend puts it. I would have guessed that a nice shiny stock image doesn't do the trick, but this helps a lot to understand why :). Will definitely take into account for next time. And yes any other tips and tricks we learn along the way let's share them :)