keep on the good work! I also like the preview video images - how do you make them? However, it is another topic.
I'm glad to see that!
All preview pictures I make in Photoshop. I've created a template, where in several tricks I located an area that is always visible (YouTube likes to crop thumbnails at the edges) and always try to place the image and inscriptions in this area. I take sources images from loading screens, covers/advertisements (improved with neuronets) or make clipart from real photographs. Most of the time took work on the design of the GridTrouble preview. The final design was the fifth or sixth version, which I liked. But, in any case, I am discovering new techniques for working with graphics.
BTW, I've created some new unnoficial covers for games. Soon I'll start new topic at forum about that.