The EU already had a tax on video cameras that can shoot longer than 29 minutes and 59 seconds. So a megapixel tax might not be unthinkable, because with a lot of megapixels you can make a high quality copy of documents and prints and of course copy machines are taxed.
Relax, it was a joke. You seem to think taxes just exist to annoy people.
There will not be a megapixel tax, as there is no need to incentivize people to shoot with lower resolutions. As was already pointed out, multiplying documents can be done a whole lot easier than with cameras.
Just as there is no point anymore in the recording length tax, which is why it also does not exist anymore. As far as I know, it came from the time when camcorders could be used to easily record and copy movies and TV, which certain lobbying groups have an interest in discouraging.
As for the rain water, as far as I'm aware that is a control tax to discourage people from sealing all their property and thereby increase the public cost of canalization.
The market is poor at accounting for public or long term cost, hence taxes exist to at least partially discourage certain behaviors without banning them.