openclaw - 💡(How to fix) Fix Inbound images from Slack exceed Anthropic 5MB base64 limit (no auto-resize) [1 participants]

Bug

Images sent via Slack are stored raw (Slack does not compress uploads like Telegram does). When the image is between 5MB and 6MB, it passes OpenClaw's MAX_IMAGE_BYTES (6MB) check but gets rejected by Anthropic's API:

LLM request rejected: messages.107.content.1.image.source.base64: image exceeds 5 MB maximum: 5387944 bytes > 5242880 bytes

The same image sent via Telegram works fine because Telegram compresses photos automatically before delivery.

Root Cause

MAX_IMAGE_BYTES in src/media/constants.ts is set to 6MB, but Anthropic's base64 image limit is 5MB (5,242,880 bytes).

The optimization pipeline in loadWebMedia (src/web/media.ts) targets the 6MB cap, so images between 5-6MB pass through but are rejected by the provider.

Suggested Fix

Quick fix — lower the constant:

// src/media/constants.ts line 1
// Before:
export const MAX_IMAGE_BYTES = 6 * 1024 * 1024; // 6MB

// After:
export const MAX_IMAGE_BYTES = 5 * 1024 * 1024; // 5MB – matches Anthropic base64 limit

This ensures optimizeImageToJpeg / optimizeImageWithFallback in src/web/media.ts will resize any image above 5MB before it reaches the LLM.

Better fix — make the limit provider-aware:

Different providers have different limits (Anthropic 5MB, OpenAI 20MB, Gemini 20MB). Ideally the optimization cap should come from the target model's constraints rather than a single global constant. This would avoid unnecessarily downscaling images for providers that accept larger payloads.

Reproduction

1. Send a 5-6MB image via Slack DM to an OpenClaw bot using an Anthropic model
2. Observe the image exceeds 5 MB maximum error
3. Send the same image via Telegram — works fine (Telegram compresses to ~1-2MB)

Environment

• OpenClaw version: 2026.2.6
• Channel: Slack (socket mode)
• Model: anthropic/claude-opus-4-6