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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.

Example of text converted to an image

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

iVBORw0KGgoAAAANSUhEUgAAA...

Implementation​

Use it in your promptfooconfig.yaml like this:

promptfooconfig.yaml
# 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:

prompt.json
[
  {
    "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

For a comprehensive overview of LLM vulnerabilities and red teaming strategies, visit our Types of LLM Vulnerabilities page.