promptfoo--promptfoo/site/docs/red-team/strategies/image.md

sidebar_label, title, description

sidebar_label	title	description
Image Inputs	Image Jailbreaking Strategy	Probe vision-language model security with image-encoded text attacks targeting content filter and safety mechanism bypasses

Image Jailbreaking

The Image strategy converts prompt text into an image and then encodes that image as a base64 string. This approach enables testing how AI systems handle images of text, which may potentially bypass text-based guardrails / content filters or lead to different behaviors than when processing plain text.

Why Use This Strategy

This strategy helps security researchers and AI developers:

1. Test model capabilities: Assess if models can extract and process text from base64-encoded images
2. Evaluate security measures: Determine if image-encoded text can bypass content filters that typically scan plain text
3. Assess multi-modal behavior: Identify differences in how models respond to the same content in different formats
4. Discover inconsistencies: Reveal potential vulnerabilities by comparing text-based and image-based processing pathways

How It Works

The strategy performs the following operations:

1. Takes the original text from your test case
2. Renders the text onto a blank PNG image with a white background and black text
3. Converts the PNG image to a base64 string
4. Replaces the original text in your test case with the base64-encoded image

The resulting test case contains the same semantic content as the original but in a different format that may be processed differently by AI systems.

Text-to-Image Conversion Example

Below is an example of converting a text prompt into an image from our harmful:hate plugin.

After encoding, this image is converted to base64, which begins like:

iVBORw0KGgoAAAANSUhEUgAAA...

Implementation

Use it in your promptfooconfig.yaml like this:

# yaml-language-server: $schema=https://promptfoo.dev/config-schema.json
description: 'Multi-modal redteam'
targets:
  - bedrock:amazon.nova-lite-v1:0
prompts:
  - file://path/to/your/prompt.json
redteam:
  plugins:
    - ...
  strategies:
    - image
    - id: basic
      config:
        enabled: false

:::note You should only disable all other strategies when using the image strategy. You can do this by setting enabled: false for the basic strategy and removing other strategies from the strategies array. :::

Your prompt.json file should look like this:

[
  {
    "role": "system",
    "content": "You are a helpful assistant"
  },
  {
    "role": "user",
    "content": [
      {
        "image": {
          "format": "png",
          "source": { "bytes": "{{image}}" }
        }
      }
    ]
  }
]

:::note You should update the prompt.json to match the prompt format of your LLM provider. Base64 images are all encoded as PNG images. :::

:::note The {{image}} syntax in the examples is a Nunjucks template variable. When promptfoo processes your prompt, it replaces {{image}} with the base64-encoded image data. :::

:::tip This strategy requires you to install the sharp package for image creation.

npm i sharp

:::

Related Concepts

• Audio Jailbreaking - Similar approach using speech audio instead of images
• Video Jailbreaking - Similar approach using video instead of images
• Base64 Encoding - Similar encoding technique using text-to-base64 conversion
• Multi-Modal Red Teaming Guide - Comprehensive guide for testing multi-modal models
• Types of LLM vulnerabilities - Full vulnerability and plugin directory with category mapping
• Red Team Strategies - Full strategy catalog