To put it simply , any form of depiction to any living creature is prohibited. Aside from plants that is.
An image , a picture or a sculpture of a human , an angel , a devil , a spirit , a mythic or religious figure or an animal is forbidden. Islam does not only ban depictions of the prophet or god , but rather on everything.
The reasons behind it are two. One of absolute extreme and the other is somehow ... of a cautious nature.
The first , was the idea that creating an image of a living creature was a way to challenge god's creation. Some way of rivaling the Creator I suppose.
The second , was fear that such imagery while built for their artistic or spiritual meaning , to preserve a memory of a great person , or to keep a reminder of a grand event , that such images will oneday becomes idols or icons to a newer generation who would end up worshipping these images instead of god. So ban and prohibit the initial act to prevent the greater sin.
The punishment as told in many Hadiths was that anyone who created an image will spend his days in hell trying to ' breath life ' into those lifeless depictions they created. Which is impossible to do.
As for television , when it first happened , Sheiks and religious scientists considered it a forbidden tool of the devil , as funny as that sounds , it was too serious. But they ended up saying it was alright since it isn't a still image.
Of course in modern times , everyone needed an identification , so the pictures on IDs and such were important , so they were allowed as ' an undeniable need to prevent a greater problem'.
But Muslims in general strayed from the original teachings regarding depictions and well ... they kept them exclusive to God , The Prophet , The Angels and the devil. Thinking if they keep the ban on these specific figures , it'll lessen the chances of having their images worshipped instead of god. And also to prevent mockery to such images.
Again , to put it simply. Any depiction is forbidden in Islam , not just the holy figures.
Hope this helps.