I found a screenshot on another forum and was not able to get an ID on the user's HUD. Can anyone assist me on this matter, please? I apologize, in advance, for the lack of resizing since I haven't much experience in these matters.

I'm not seeing a HUD in this picture.  A HUD is usually a set of circles or rings around the toon (usually the center of the screen). 

If you are talking about the mods in the UI, it looks to me like KGpanels with simple minimap, bartender or dominos and sl data text and probally pitbull for the unit frames