If "New account created" is passive. Why there not "account was/is created"? I have seen a lot of similar examples.
It's very common in English to omit little things like articles and different forms of the verb to be in situations where being concise and to the point is more important than being syntactically complete which is very common in public signage, Internet notification messages, graphical user interfaces and things of that nature. While you don't really lose anything in meaning, that way things certainly become easier and faster to read. And that, believe it or not, is the whole point of it.
I'm not one hundred percent sure if this is directly related to something called headlinese (the same thing done with news article titles and headlines), but the concepts are no doubt very similar. For example, instead of saying "The NASA astronaut who was the first to fly untethered in outer space dies at the age of 80", a typical news headline would read:
NASA astronaut, 1st to fly untethered in space, dies at 80
It's a form of "headlinese" or "telegraphese".
The form of "to be" ("is" or "was") can be omitted when there is little space. For example a newspaper headline could read:
Trump and Clinton working to flip states in their favor
New skyscraper biggest in world
In both cases a form of "to be" has been omitted.
As you note the same thing can be done with a passive particle:
New window created.
This sort of clipped speech creates potential ambiguities, which are resolved pragmatically from the context.
One would have to rely on context to decide if that means "John was omitted", or "John hopped and danced as he was walking."