Doctor Eggman Nega's camera is the primary plot device that drives the story in Sonic Rivals. While appearing as a normal camera, it is actually a highly advanced piece of technology from approximately two hundred years into the future. Any object that this camera takes a picture off will instantly be converted into a card.
In Sonic Rivals, Eggman Nega's master plan was to use this camera to alter his family's history by erasing his ancestor Dr. Eggman and his failures from the world so that his brilliance would be recognized in the future. He was however stopped by Sonic the Hedgehog, Knuckles the Echidna, Shadow the Hedgehog and Silver the Hedgehog.
On the front, Dr. Eggman Nega's camera appears as a regular, multi-colored digital camera, which only serves to cover for its more dastardly purposes. Any target that the user chooses to take a picture of with this camera, whether it is an inanimate object or living being, will then be converted into an inanimate, two-dimensional card. As speculated by Tails, the camera is able to "break down matter at the atomic level, allowing it to be stored as digital card media."
Living beings that are turned into cards by this camera are seemly locked in some kind of stasis while only being semi-aware of the happenings around them while in card form. Objects with certain properties, such as the Master Emerald, that are turned into a card by this camera, allows the holder of such cards to manipulate the properties of the said object.
While it has not been explained how objects captured by Dr. Eggman Nega's camera can be returned to normal, it appears that the conversion happens independently and according to the holder of the cards' will; when Sonic acquired Tails and Amy Rose's cards, he was seemingly able to return them to normal in the following cutscene.
Created at some point in the future thanks to this era's advanced technology, it is unknown whether this camera was one of Dr. Eggman Nega's own creations or that the doctor stole it from somewhere (though Silver's statements might confirm the latter). Having his genius and honor of coming from a lineage of brilliant scientists denied due to the historic failures of his ancestor Dr. Eggman, Eggman Nega acquired this camera and decided to change his family's history by using the camera to trap the present-day Dr. Eggman inside a card, thus allowing Eggman Nega to take control of his own destiny.
Prior to the events of Sonic Rivals, Dr. Eggman Nega used his camera to photograph the Master Emerald in his time, trapping it in a card so that he could use its powers for his own purposes; however, due to the Master Emerald existing simultaneously across the time-space continuum, this act resulted in the Master Emerald disappearing in all time lines as well, even in front of Knuckles the Echidna's eyes in the present as well. Eggman Nega then used the Master Emerald card to teleport Onyx Island (the future of Angel Island) to Sonic's time to serve as his vehicle through the time stream. However, Silver the Hedgehog learned of Eggman Nega's use of the camera and followed the doctor into the past to prevent Eggman Nega from using the camera's power to wreak havoc.
In Sonic's time, Dr. Eggman Nega did not waste any time and began to use his camera to turn various other objects to cards as well. When Tails, Amy Rose and Rouge the Bat later arrived at Onyx Island, Eggman Nega turned them into cards as well with his camera, to keep them from meddling in his plans, before finally succeeding in capturing his target, Dr. Eggman in a card with his camera as well.
Over the course of the game, Eggman Nega suffered several defeats and setbacks at the hands of Sonic, Knuckles, Shadow and Silver. Eventually, Eggman Nega finally snapped, going into an insane frenzy and decided to turn the entire Earth into a card with his camera; while it would endanger Eggman Nega's existence and the fate of the world as well, Eggman Nega cared not for this as if he could not have the future, then no one could. Escaping to Meteor Base Zone, Eggman Nega mounted his camera to his spaceship, the Egg Destroyer and planned to charge the camera with the cards containing Amy, Rouge and the Master Emerald. As Eggman Nega took off in the Egg Destroyer to achieve his insane goal, however, Sonic, Knuckles, Shadow and Silver managed to stop the doctor's vessel, causing Eggman Nega to lose control of the camera and got turned into a card himself, while the heroes managed to free all of Eggman Nega's captives in the cards.
What happen to Doctor Eggman Nega's camera afterwards is unknown; either it was destroyed, lost during the final battle or it was reclaimed by Silver, who took it back to the future.
- The camera provides an in-story rationale for the collectable cards that are picked up over the course of Sonic Rivals.