Larian Studios Forums Divinity - Original Sin Divinity Original Sin - Mods HQ/Original art for the character portraits?

Make sure you have the latest version of Microsofts Visual C++ Runtime installed. Norbyte posted a link to it in one of his more recent threads.

Icons are all in the Icons.pak file. There are several .dds files.

You can edit .dds files with Photoshop or use Gimp with the DDS-Plugin, that's what I use to edit .dds files.
There might be other programs for editing .dds files which I do not know about.