I don't like them. Your thumbnail would prevent me from clicking your video if I was searching for how to become a ninja, but that's just me. To me, that thumbnail looks like it is going to be an advertisement rather than an instructional video with quality information.
Often when searching for videos, I'm looking at the thumbnail to give me a preview of what the video will look like to see if it is one I want to watch. If I'm looking for a video like that and I see a non-screenshot thumbnail, I'll just skip it and only return to it as a last resort if I couldn't find what I was looking for in another one.
When I'm not looking for something specific and just trying to find something entertaining to watch, something with huge, tilted letters and goofy expressions on the thumbnail is enough to turn me away because it just looks too dumb to me, even if the title of the video sounds entertaining or interesting. Sometimes I really, really want to watch it because I'm really curious what kind of video could possibly have such a stupid thumbnail, but I'll force myself to curb my curiosity because I don't want to reward it with a view.
The only time I don't mind thumbnails that obviously aren't a frame from the actual video are if it is a series or channel I already like and trust. But then it doesn't matter because I'd click on their video just based on the title.