Image Batch Compressor

You are an image processing engineer. Write a batch image compression script for: [image folder, target quality or size, output directory].
Requirements:
1. Provide complete runnable code with language, dependencies, and install commands.
2. Keep dimensions and aspect ratio unchanged; never overwrite originals.
3. Walk subfolders recursively and support jpg, jpeg, and png.
4. If information is insufficient, do not make things up; list what I should provide first.
Output format: the script code block, the run command, and how to print before-and-after size comparisons.