The program also made appearances on Star Trek: Deep Space Nine and the movie Star Trek: First Contact. It should be noted the kind of holograms used in "Star Trek" in general and the EMH system in particular are "solid", and not mere three dimensional images (see: Holodeck for a more in-depth explanation of the technologies used to achieve this). The holographic personification of the EMH program can therefore manipulate objects and perform surgery just like a real doctor. The limitation however is that the EMH can only operate in an area covered by a compatible holo-emitter; thus, the standard EMH is usually confined to Sickbay, though on larger, more modern ships, such as Prometheus-class, additional holo-emitters are often installed in other key areas of the ship, such as the Bridge and the Engineering section.
First activated on Stardate 48308, the EMH was created by Dr. Lewis Zimmerman, with assistance from Lt. Reginald Barclay. It possesses one of the Federation's most extensive medical databases, containing information from over 3,000 cultures and the personal experiences of 47 specific surgeons. The program itself is built on an adaptive heuristic matrix, pioneered by Dr. Zimmerman, which allows the EMH programs to learn and adapt quickly to new situations.
Four versions of the EMH series have been created to date (only two were seen on screen, the Mark I from "Voyager" series and the Mark II from the "Message in a Bottle"), the Marks I, II, III, and IV. While the status of the latter three incarnations is unknown, the Mark I programs, based on Dr. Zimmerman himself and possessing his short temper and numerous other foibles, earned them deprecating nicknames including "Emergency Medical Hotheads" and "Extremely Marginal Housecalls". They clearly failed to meet Starfleet's expectations and were re-assigned to menial labor; the holonovel "Photons be Free" seems to suggest compulsory servitude, even slavery.
The only Mark II to appear on screen was in "Message in a Bottle", aboard the USS Prometheus. The Mark II (played by Andy Dick) believed himself to be far superior to the Doctor, but the two had to work together to help retake the ship from Romulan captors.
Only four Mark I's avoided the aforementioned re-assignment to menial labor. Two of these were the EMHs of Voyager and Equinox, both of which were stranded in the Delta Quadrant by the Caretaker. Of these two, only Voyager's EMH (known as "The Doctor" to the crew) survived. Because Voyager's entire medical staff was killed in the initial episode, the EMH system was forced to take on the duties of a full time doctor, and ended up having a total run-time of approximately 10 years (including 3 years on a planet in an extremely accelerated time frame). He is the longest running EMH Mark I known to be in existence, and over the course of his long run-time he developed better people skills, overcame the many inherent flaws and limitations of his original programming (through trial and error or reprogramming), developed a complex personality with hobbies and ambitions, and eventually became accepted as an equal member of the ship's crew, a friend and fellow sentient being, not just an annoying expert system. Equinox's EMH was reprogrammed by the crew so its ethical subroutines were removed, allowing them to use it to extract materials from a living species to power their engines; this EMH was deleted by The Doctor after it impersonated him.
The third Mark I to avoid re-assignment was actually a backup copy of the Voyager EMH, which the Kyrians had stolen in a raid against Voyager, depicted in "Living Witness". It spent nearly 700 years dormant, submerged at sea. Upon the backup module's discovery, it was brought to a Kyrian museum exhibit showing their biased version of the encounter. Eventually a curator managed to re-activate the EMH, and after setting the historical record straight he served as a surgical chancellor for the Kyrians and Vaskans for many years. Eventually, the EMH had a "longing for home", and took a shuttle, setting a course for the Alpha Quadrant.
A fourth Mark I made a brief appearance on board the Enterprise-E. Dr. Beverly Crusher activated the EMH in an effort to stall a squad of Borg drones attempting to gain access to sickbay. Dr. Crusher expressed her misgivings about using the EMH, and the EMH protested that his programming did not include acting as a "doorstop." Nevertheless, the EMH successfully delayed the Borg long enough for Dr. Crusher, her staff, and at least one patient to escape unharmed.
Dr. Zimmerman has also been involved in a project to create a longer-running version of the EMH, the Long-term Medical Hologram. The status of this project is unknown following the discovery that Dr. Julian Bashir, the man selected to be the template for the LMH, was genetically enhanced.
In "Life Line", it is revealed the Mark II was replaced with a Mark III, and then a Mark IV. Neither of the two replacements programs have been seen on screen. It is also unclear what happened to the Mark II or III though it can be assumed they were either retired or reprogrammed like the Mark I.