An MCP server is an add-on program that gives Claude extra tools. CLAUDE_CODE_TOOL_PICTURE_SERVERS is a new environment variable, a named value you set in your shell before starting Claude Code, that lists MCP servers by name.
For a server on that list, when a tool result is marked with anthropic/deliverImages, Claude Code adds a note for Claude: "The pictures in this result are shown to the user with your reply, so they need no sending." This applies only in the main conversation, not in helper agents, and depends on a couple of further conditions.
Why
This gives MCP servers an opt-in way to hand pictures to you alongside Claude's reply. Claude is told not to try to pass them on itself.
