What is the best image size for a background image?
The best size depends on the environment in which you're planning to use the widget, and what the image itself is like.
If all your students are on iPads, a good size is 1024x768, and the image will always be fully displayed. If your students are going to use your widget in a browser, this is generally also a good size. If use will be mostly on cellphones, for most widget types it's better to use a portrait style image, e.g. 720x1280.
- Original image size: in this case the original image size is used and the image is tiled horizontally and vertically
- Contain full image: the entire image will be displayed in the available space. In most cases horizontal or vertical borders will be present, depending on the aspect ratio of your image and the display window for the widget
- Cover complete area: in this case the image will be centered and resized so the full area is covered. Usually either horizontally or vertically a piece of the widget will be cut off. This depends on the image aspect ratio and the widget display window.