If you are using directadmin and want enable webp support (Centos OS)
yum install libwebp-devel
vi /usr/local/directadmin/custombuild/custom/fpm/configure.php71
--with-webp-dir=/usr/lib64
./build php
If you have php 5.6 so use --with-vpx-dir


php -r 'var_dump(gd_info());'
array(12) {
  ["GD Version"]=>
  string(26) "bundled (2.1.0 compatible)"
  ["FreeType Support"]=>
  bool(true)
  ["FreeType Linkage"]=>
  string(13) "with freetype"
  ["GIF Read Support"]=>
  bool(true)
  ["GIF Create Support"]=>
  bool(true)
  ["JPEG Support"]=>
  bool(true)
  ["PNG Support"]=>
  bool(true)
  ["WBMP Support"]=>
  bool(true)
  ["XPM Support"]=>
  bool(false)
  ["XBM Support"]=>
  bool(true)
  ["WebP Support"]=>
  bool(true)
  ["JIS-mapped Japanese Font Support"]=>
  bool(false)
}

If you do not use fpm, so:
./build used_configs | grep configure.php
PHP (default) configuration file: /usr/local/directadmin/custombuild/configure/ap2/configure.php56
cd /usr/local/directadmin/custombuild
mkdir -p custom/ap2
cp -fp configure/ap2/configure.php56 custom/ap2/configure.php56