You're referring to Flipnote Studio and its ROM (Read-Only Memory)!
Flipnote Studio is a free, web-based animation software developed by Nintendo for the Nintendo DSi and Nintendo DSi XL handheld consoles. It was released in 2009. The software allowed users to create and share animations, called "flipnotes," using a series of still images. flipnote studio rom
Regarding the ROM, I assume you're asking about the software's internal workings or perhaps a hack-related project. Here are some insights: You're referring to Flipnote Studio and its ROM