For those using Windows 10 with PHP 7 the following might help:
determine whether your Windows is threadsafe (see the output of phpinfo()) and 32 or 64 bits.
This page contains matching sets for each php version and threadsafe and 32/64 settings. Download both the Imagick and the Imagemagick files.
Follow for Imagick the instructions at the bottom of that page.
For ImageMagick the instructions on that page are not correct. You can put the dll files anywhere but you need to refer to them with the MAGICK_HOME windows environment variable. You may need to reboot for the change of the environment to have effect.