Starting with Strategy Mobile iOS 9.3, it is possible to customize icons of the Multimedia Widget and display a thumbnail image file instead of the default icons for supported content formats.
Please refer to "Strategy Mobile Design and Administration Guide" for detailed information about the capabilities and steps on how to use the multimedia widget. The product manual can be found online, clicking on Product Manuals on the right hand side. As described in the documentation the following columns are required for the Multimedia Widget to function properly:
In order to add a thumbnail to the respective content, a seventh column needs to be added and placed to the right of MW_Description and containing values with the path to the image location: