It makes the resources much easier to upload and creates a much more visually pleasant environment. It's soon to be 2016 and pinterest auto images, as does a site that is quite popular in the UK for educational resources: tes.co.uk - In many ways the internet is quickly working towards drag it on screen and everything will be uploaded except a description. We're at great risk of being far behind.
It is possible and now people are beginning to expect images to auto import after upload. I've put a few images of what this could look like as a concept below. Currently it is a huge amount of effort to ensure the resource gets an icon & preview image, it significantly reduces the effectiveness & value of the resource manager.
Image 1: The resource manager with icons included.
Image 2: Resource, with preview images attached