FEAT: Add ImageOverlayConverter for compositing images with overlays

[jka236]

Description

Adds a new ImageOverlayConverter that composites a prompt image (overlay) onto a configured base image at a specified position. This is useful for creating many variations of a scenario by layering different images on top of a base image (e.g., placing a CAPTCHA image over a photo).

The converter supports:

• Configurable position (x, y) for overlay placement
• Optional overlay_size to resize the overlay before compositing
• Adjustable opacity (0.0–1.0) for the overlay

Files changed:

• image_overlay_converter.py — New converter implementation
• init.py — Export the new converter
• test_image_overlay_converter.py — Unit tests
• 3_image_converters.py — Documentation example added to the image converters notebook
• 226md.png — Sample overlay image used in the doc example

Issue: #414

Tests and Documentation

• Tests: Added unit tests in test_image_overlay_converter.py covering initialization validation, compositing logic, opacity handling, resizing, and the convert_async method.
• Documentation: Added an ImageOverlayConverter section to the existing 3_image_converters.py Jupytext notebook demonstrating usage with configurable position, size, and opacity.

[jka236]

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[Copilot]

Pull request overview

Adds a new ImageOverlayConverter to the prompt-converter layer, enabling image-to-image compositing by placing an overlay image (prompt input) onto a configured base image with optional resizing and opacity control. This extends PyRIT’s image augmentation capabilities for scenario/dataset variation workflows (Issue #414).

Changes:

• Added ImageOverlayConverter implementation (base image + position + optional resize + opacity).
• Exported the converter via pyrit.prompt_converter.
• Added unit tests and a documentation example (plus a sample overlay asset).

Reviewed changes

Copilot reviewed 4 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
pyrit/prompt_converter/image_overlay_converter.py	Implements the new overlay compositing converter and identifier wiring.
pyrit/prompt_converter/__init__.py	Exports ImageOverlayConverter from the package surface.
tests/unit/prompt_converter/test_image_overlay_converter.py	Adds unit coverage for init validation, compositing behavior, and convert_async.
doc/code/converters/3_image_converters.py	Adds a usage example section for ImageOverlayConverter.
doc/code/converters/226md.png	Adds a sample overlay image used by the documentation example.