Centos 7 – Upgrade ImageMagick

Too long for a comment:

AFAIK it has only been less then a day since the CentOS 7.4 update has been released and your local mirror may not be synched yet. You may need to wait a little bit for the latest updates to become available locally.
You may try a yum clean all to prevent cached results after checking that the Update repositories haven't been disabled.

Assuming your yum repositories are correctly configured yum update is sufficient to keep your system up to date and secure and there is no need to build software from source.

Please read the vendor (CentOS is derived from Red Hat Enterprise Linux) explanation of backporting security updates and bug fixes and what is the impact on version numbers.

This answer is an explanation of the big mis-understanding on what security scanners detect, report and recommend and how that often conflicts with back porting.

You've mixed a whole bunch of manually downloaded RPMs (some built for the wrong versions of PHP, Imagick or other things) and conflicting repositories. Stop now. Don't manually download RPMs.

You've done well to use Remi's PHP repositories, but you've enabled his repo for PHP 5.6, while you say you want PHP 7.0. You need to disable the remi-php56 repo and enable the remi-php71 or remi-php72 repo (7.0 is EOL, don't use it).

After getting the correct repo enabled, use yum distro-sync to replace all the wrong versions of packages with correct versions of packages. You'll also need to remove some packages you got from SCL or other repos, such as those with names starting with php70-.

Finally, you can get to installing the package you were looking for:

[root@llothien ~]# yum install php-pecl-imagick
Loaded plugins: product-id, search-disabled-repos, subscription-manager
epel/x86_64/metalink                                     |  14 kB     00:00     
epel                                                     | 3.2 kB     00:00     
error-rl                                                 | 3.0 kB     00:00     
mariadb                                                  | 2.9 kB     00:00     
nginx                                                    | 3.5 kB     00:00     
remi                                                     | 2.9 kB     00:00     
remi-php72                                               | 2.9 kB     00:00     
remi-safe                                                | 2.9 kB     00:00     
rhel-7-server-extras-rpms                                | 3.4 kB     00:00     
rhel-7-server-optional-rpms                              | 3.5 kB     00:00     
rhel-7-server-rpms                                       | 3.5 kB     00:00     
saltstack-salt                                           | 3.0 kB     00:00     
(1/12): epel/x86_64/updateinfo                             | 933 kB   00:00     
(2/12): epel/x86_64/primary                                | 3.6 MB   00:00     
(3/12): mariadb/primary_db                                 |  61 kB   00:00     
(4/12): remi-php72/primary_db                              | 195 kB   00:00     
(5/12): rhel-7-server-extras-rpms/x86_64/primary_db        | 420 kB   00:00     
(6/12): rhel-7-server-extras-rpms/x86_64/updateinfo        | 273 kB   00:00     
(7/12): remi/primary_db                                    | 2.2 MB   00:00     
(8/12): remi-safe/primary_db                               | 1.3 MB   00:01     
(9/12): rhel-7-server-optional-rpms/7Server/x86_64/primary | 7.2 MB   00:00     
(10/12): rhel-7-server-optional-rpms/7Server/x86_64/update | 2.1 MB   00:00     
(11/12): rhel-7-server-rpms/7Server/x86_64/updateinfo      | 2.9 MB   00:00     
(12/12): rhel-7-server-rpms/7Server/x86_64/primary_db      |  55 MB   00:01     
epel                                                                12647/12647
Package php-pecl-imagick-3.4.3-10.el7.remi.7.2.x86_64 already installed and latest version
Nothing to do
[root@llothien ~]#