Agents get avatars from presets or an uploaded image
In the UI: open an agent’s Branding sheet. Drop a PNG, JPEG, GIF or WebP image on the avatar and position the square crop, or use Choose preset to search 25 curated avatars and save one with Use avatar.
In code: PUT /v1/agents/{agent_id}/avatar uploads an image as the
multipart field file, and PUT /v1/agents/{agent_id}/avatar/preset selects a
preset. The agent’s avatar field lists public, immutable image URLs. The A2A
Agent Card carries it as iconUrl, and one-click Slack apps use it as their icon.