If you prefer a direct link, you can try the following:
gpg --verify imagemagick-7.1.1-15.tar.gz.sig
How to install the latest version of ImageMagick? - Ask Ubuntu imagemagick 7.1.1-15 download tar.gz
tar -xzf ImageMagick-7.1.1-15.tar.gz cd ImageMagick-7.1.1-15
./configure make
After downloading, verify the integrity of the download using the SHA-256 checksum:
cd imagemagick-7.1.1-15
curl -O https://imagemagick.org/archive/ImageMagick-7.1.1-15.tar.gz