Recently I have tried to install imagemagick application on Ubuntu.
I tried to download it from home page and install the latest version of it.
However it did not actually worked as planned.
So the easiest way is to just install from ppa
sudo apt-get install imagemagick
Other ways may require to install some extra stuff to make it work
e.g.
jpeg libraries or png ones in order to make convert or other executable binaries to make it work as expected.