AI agents use add-watermark to create or update resources in MCP Media Processing Server — usually the action step of a workflow, after the agent has gathered context. Every call changes real data in your MCP Media Processing Server environment.
This tool modifies image data by adding a watermark overlay, which is a reversible change (the watermarked image is new/modified but the original remains and the watermark can be removed). It does not execute arbitrary code, delete data, or perform financial operations. It fits the Write category—creates or modifies data reversibly.
From the tool's definition Tool adds a watermark to an image, which modifies the image data. The description states 'Add watermark to image' indicating a write operation that alters the image content.
Documented attack patterns abuse exactly the kind of access add-watermark gives an agent:
PolicyLayer is an MCP gateway — it sits between your AI agents and MCP Media Processing Server, and nothing reaches the server without passing your rules. This is the rule we recommend for add-watermark:
{
"version": "1",
"default": "deny",
"tools": {
"add-watermark": {
"limits": [
{
"counter": "add-watermark_rate",
"window": "minute",
"max": 30,
"scope": "grant"
}
]
}
}
}add-watermark stays usable, but capped — an agent stuck in a loop can't make hundreds of changes a minute. Everything else on the server is denied unless you say otherwise.
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Add watermark to image. It is categorised as a Write tool in the MCP Media Processing Server MCP Server, which means it can create or modify data. Consider rate limits to prevent runaway writes.
Register the MCP Media Processing Server MCP server in PolicyLayer and add a rule for add-watermark: allow, deny, rate-limit, or require approval. Point your MCP client at the PolicyLayer proxy URL and the rule is enforced on every call, before it reaches MCP Media Processing Server. Nothing to install.
add-watermark is a Write tool with medium risk. Write tools should be rate-limited to prevent accidental bulk modifications.
Yes. Add a rate_limit block to the add-watermark rule in your PolicyLayer policy. For example, setting max: 10 and window: 60 limits the tool to 10 calls per minute. Rate limits are tracked per agent session and reset automatically.
Set action: deny in the PolicyLayer policy for add-watermark. The AI agent will receive a policy violation error and cannot call the tool. You can also include a reason field to explain why the tool is blocked.
add-watermark is provided by the MCP Media Processing Server MCP server (maoxiaoke/mcp-media-processor). PolicyLayer sits as a proxy in front of this server to enforce policies before tool calls reach the server.
Start from MCP Media Processing Server, add the rest of your stack, and see everything your agents can call. Then put policy on all of it.
Free to start. No card required.
10 MCP Media Processing Server tools catalogued and risk-classified — across an index of 43,000+ MCP servers.