Yes, i've got that error when loading verification images at my website. So, what should i do?

Check the GD lib installed on your linux box.

Try to reconfigure PHP with additional configure like this :

        --with-zlib \
        --with-gd \
        --with-png-dir=/usr/lib \
        --with-jpeg-dir \

 Reinstall PHP with new configuration

 root@linux~# make && make install

How to install latest GDLibrary ?

1. Download file at here

2. Install  GD Library

./configure && make && make install

3. Install PHP with options above

Note :

Sometimes, we've got an error messages like this :

Call to undefined function imagettfbbox()

The solutioons :

1. Try to recompile your PHP with including --with-freetype-dir=/usr/include/freetype2/freetype \

2. Don't forget "make clean" instead.

Good Luck