Developing a Solidity application with an image struct, I ask: does storing image data in a custom structure make it an NFT, or must ERC721 and metadata be utilized?
Storing image data in a custom structure is essentially just a method for organizing your data, and does not automatically classify it as an NFT. An NFT must follow a standard like ERC721 which establishes token ownership, metadata protocols, and transfer capabilities. In my experience, while custom structs can serve specific purposes, integrating with a recognized token standard is essential for achieving full non-fungible functionality and market interoperability. Without this adherence to standard practices, you lose many advantages associated with NFTs.