Your photo and your cover image
The photo. Tap the camera button on the card header in the editor. A face, framed close, looking at the camera. Not a logo: people trust a person, and the card exists to make you memorable.
The cover. The band behind your photo. A workspace, a product, your shop front, or a flat colour. Landscape, wide — roughly 1600 by 470 — and nothing important in the centre, where your photo sits.
A video cover. An .mp4 or .webm works as a cover and plays quietly on loop. Keep it under a few seconds and under a megabyte or two: it is the first thing to load on a phone.
Where they come from. Upload from your phone, pick a stock photo, or generate one — the picker offers all three.
In a team. If your leader locked the cover image, the button is not shown: the team's banner is the same on every card, on purpose.