Any other images just download and make sure there is NOT a background in the image.
When you have your .dds file open, drag and drop your portrait over the the existing .dds. You MUST keep the black background for CSPs and RSPs or you will have horribly rendered images ingame. Fix, scale, recolor to your liking. When done save your .dds file. Format extensions below.
Format 0 and 1 – DXT1_ARGB or DXT5_ARGB
Format 2 – DXT3_ARGB (I use DXt5_ARGB for format 2)