Stand-in image for previews and any other spot that needs a reference visual when a real image slot is unresolved.

Ships as a data URL — no static file serving to configure, and it works everywhere <image href="…"> accepts a data: scheme (browsers, resvg, and every rasterizer we use).

The design is intentionally boring — a light-gray square with four arrows radiating from the center to the corners, plus a small "Placeholder image" caption. Zero brand, zero color, zero risk of being mistaken for real content.