Some modern modding tools like Open PS2 Loader (OPL) use VMCs. While these are images, they are sometimes formatted differently than the ones used by desktop emulators like PCSX2.
Enter the third parties: Mad Catz, Interact (GameShark), Hip Gear, and dozens of white-label brands. not a ps2 memory card image
The most famous "non-PS2 card" wasn't a storage device at all, but a hacking tool. The GameShark 2 and Action Replay Max utilized specialized memory cards that had boot code burned into them. You would insert the disc and the card; the card would tell the PS2 to bypass the disc check, allowing you to boot into a cheat menu. These cards were essential for the scene, allowing players to unlock debug menus, play burned games (via the "swap trick"), and apply infinite health cheats. Some modern modding tools like Open PS2 Loader