As of January 1, 2024, the earliest version of Mickey Mouse from the 1928 short Steamboat Willie entered the public domain, meaning you can technically use that specific, black-and-white, "rat-like" iteration of the character on a shirt without permission from Disney. However, in 2026, you must navigate a "High-Fidelity" legal minefield: Disney still holds the copyright for all later versions of Mickey, including his more modern neotenous appearance, white gloves (added in 1929), and red shorts. Furthermore, Mickey Mouse remains a protected trademark, meaning you cannot use him in a way that suggests your product is an official Disney product or misleads consumers about the source of the goods. If your shirt design creates "brand confusion," Disney can still sue for trademark infringement. To be safe, any commercial use of Mickey should stick strictly to the 1928 aesthetics and avoid the "Disney font" or any other high-fidelity brand identifiers that remain under the company's strictly enforced intellectual property protections.