Although Butler currently can't change a card's cover directly via an Action, you can do it indirectly using Butler's HTTP requests Action to send a suitable PUT request to the Trello REST API to update the card and set the values you want for the cover.
Refer to this recent question where I describe how to do it. You can modify that method described to set the card's cover to be an image. The image needs to be either attached to the card or an Unsplash image.
Congratulations to @Laura Holton , our latest winner of Taco Tuesday! And thanks to @Kristján Geir Mathiesen for sharing the picture of Taco having fun with his new friend B...
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