I've made artifacts/image.png: a 512 × 512 PNG with a flat yellow square centered on a near-black background. I checked the pixels and looked at the image, and nothing in the request is unmet.

• Format: 8-bit RGB PNG with no transparency, 512 × 512.
• Colors: only #f4c430 (the square) and #0e0e12 (the background) appear. There are no gradients, shadows, borders, text, other shapes, or blended edge pixels.
• Square: 396 × 396 px, running from pixel (58,58) to (453,453), which covers 59.8% of the canvas area.

I read "about 60% of the canvas" as 60% of the area. If you meant 60% of the width, the square would be about 307 px across instead.

ffmpeg wasn't installed, so I wrote the PNG with a short Python script instead. A pixel count and samples on both sides of each edge confirmed the colors and placement. I also added a short artifacts/README.md that records these details. Both files are left uncommitted, as required.