In order to attach images to phpBB2 forum posts you should install Attachment MOD which is one of the most popular MODs for phpBB.

You can have this mod installation as part of SiteGround's Exclusive Professional Services

You can order the installation of this mod from your Customer Area -> Get Support section-> HelpDesk-> Exclusive Professional Services-> Adding modules to applications

You can also install the mod yourself manually by following the instructions below:

1. Install EasyMOD in your phpBB

EasyMOD is an automatic mod installer for phpBB and we strongly recommend that you first install it and then use it to install the Attachment MOD.

EasyMOD can be downloaded from here:
http://sourceforge.net/project/showfiles.php?group_id=136984

Please, find more information about its installation at:
http://easymod.sourceforge.net/readme/#toc_g_install_EM

2. Install the Attach MOD

Installing the Attachment MOD with the help of EasyMOD is a little more complicated than installing some other MODs included in this auto-installer. However, you will be able to do it by following the instructions here:

http://easymod.sourceforge.net/readme/#faq_mod_att_inst

If you have problems installing the phpBB attachment mod yourself, you may contact your web host for assistance. SiteGround provides the best phpBB hosting and we can quickly perform the mod installation for you.