If we're going with the newspaper definition, then yes. That's why we have cases like Family Circus or Farside.
At the same time, comics as a medium are technically defined by being a collection of images juxtaposed alongside each other to create the illusion of a sequence in motion. Even comic strips use this, as they are multiple images stacked next to each other.
So technically, a single image is more accurately an illustration, and not a comic strip. At the same time, no one here will judge you for releasing single image strips.