A preview image to be shown in the Frontend Toolchain’s New tab.
There are minimum and maximum size constrains which are used to scale up/down the images, so that they are not too large or too little. It does not need to be a square image.
Currently, the recommended preview image size is 256px width, with a height
between 20px - 500px.
Typically, the type of the .NewPreview file is image-1.