What are the differences between HTML5 and (pre-5) HTML? How can I make HTML-like forms in Markdown? What is difference between Hypertext and Markup in HTML?
You set the inches and the number of pixels in each of those inches. Photoshop removes or adds data to fit the number of pixels in each of the inches you specified. Note: The original image used in the examples below is 4x4 inches, 100 ppi, 400x400 pixels at 468.8 KB.
Image size and resolution. Your custom thumbnail image should be as large as possible, as the image will also be used as the preview image in the embedded player. We recommend your custom thumbnails: Have a resolution of 1280x720 (with a minimum width of 640 pixels). Be uploaded in image formats such as .JPG, .GIF, .BMP or .PNG. Remain under the 2 MB limit. Try to use a 16:9 aspect ratio as it's the most used in YouTube players and previews.