In addition to the above answer, you can have some checks.
From your Software Center you can know the recent installed or updated apps.
And you can know which apps have imagemagick
as dependency so you can know which app had installed it.
apt-cache rdepends imagemagick
sample output:
Reverse Depends:
inkscape
graphicsmagick-imagemagick-compat
formatjunkie
graphicsmagick-imagemagick-compat
playonlinux
graphicsmagick-imagemagick-compat
lives
graphicsmagick-imagemagick-compat
variety
graphicsmagick-imagemagick-compat
|ejabberd
graphicsmagick-imagemagick-compat
imagemagick:i386
|qt4-qmlviewer
From man apt-get
rdepends pkg...
rdepends shows a listing of each reverse dependency a package has.