Group Photo Row Calculator App

I'm looking to build a web-based app to help calculate how many people in each row of a group photograph, specifically for event gatherings. The app should be compatible with both desktop and mobile browsers.

Key Features:
- Ability to process event gathering photos and determine the number of people in each row.
- Integration to point to an already produced slide for that result.

Ideal Skills and Experience:
- Experience in web app development
- Responsive design skills for both desktop and mobile platforms
- Backend development skills to manage and store data inputs

I'm looking for someone who can create a user-friendly, efficient tool for this purpose. Please provide examples of similar work done.