It seems that if you put a hidden wildlife camera in a swedish forest to make nature photos, you can be sued (if I'm not wrong). The "this is my garden" part should be taken seriously.
Not true. Anyone is allowed to take photographs and film in public spaces which should definitely include forests. Though this does not apply to installing permanent cameras in public spaces, which is much more restricted.
The main purpose of a wildlife camera-trap is to be set and left in the wild for days, weeks or months. In this sense can be called permanent. The best models are relatively expensive and can be stolen if you don't hide it carefully. Those camera are also used for fighting against environmental crimes (i.e: exposing arsonists walking the forest at 4AM minutes before a fireforest starts), so can be vandalized.
Ah, I didn't know that, thanks. In those cases you're probably correct that it's illegal to put up such camera without obtaining a permission. Though I don't think it's the law about "Kränkande Fotografering" (roughly translates to "Offensive Photography") - which is the law that makes it illegal to put up secret cameras in a home - that you'd be violating, but rather some other law that regulates surveillance cameras.