Most apps need user avatars but don't want to handle photo storage or rely on third-party services. Offer an API that generates consistent, distinctive blob avatars based on user IDs or names.
Target indie developers building social apps, forums, or productivity tools. Charge per thousand generations.
Start with a simple HTTP endpoint that returns SVG blobs, then add customization options.
The main risk is competing with free libraries, so emphasize ease of integration and distinctive art style.