When you upload or import your files into a workspace Collection, the first image to fully upload will be used as your Collection thumbnail, but you can easily change it.
There are two ways you can change a Collection thumbnail.
By assigning another file inside the Collection as the thumbnail
By copying the file ID from a file anywhere in your workspace and setting it as a Collection thumbnail.
Note: Admin and manager roles can change thumbnails on any Collection. Regular user roles can only change thumbnails on Collections they own. If you want custom roles to be able to change any Collection thumbnail, they must have Edit capability.
From inside a Collection
From inside a Collection, find the file you want to be your thumbnail and click the three-dot icon. Select Set as Collection thumbnail.
If the Set as Collection thumbnail item is greyed out, this file is already set as the Collection thumbnail.
Setting a thumbnail using a File ID
If you want to change a Collection thumbnail but there are no files in that Collection, for example, a top-level or parent Collection with multiple layers of sub-Collections, you can copy the file ID of any file and set it as the parent Collection thumbnail.
To grab a file ID, click the three-dot icon on any file and select Copy ID.
With the ID copied, navigate to the Collection you want to change. Click the three-dot icon on the Collection and select Change Thumbnail.
A modal will appear where you can place the copied file ID. Click the search icon to show your file results and select the file.
Your new file will now be visible as the Collection thumbnail.
Using files that you don't want visible to other users in your workspace
If you want to upload custom thumbnails for your Collections, for example, a logo or pre-designed graphic, but you don't want those files to live in your Collections or be visible to others in your workspace, you can create a Restricted My Collection. Find out more about My Collections here.
From the My Collections area, create a Restricted Collection and upload your files to that Collection. Make sure the files also stay Restricted! Use the method about to copy the File IDs and add them to your Collections.