Screenshot PNG to GUITexture (NONE Texture)

Hi i've looked at tens of similar issues, however when trying to use solutions that people have answered to others, it never seems to work (or i do it wrong).

What i'm trying to do is upload a PNG image generated by a unity screenshot which i have accomplished from a folder in my PC and upload it to the extent i can assign it to an already existing and placed GUITexture in gameplay, as if i've taken an image and want to view it there and then.

i've attempted time and time again the WWW methods but i never seem to get them right and has become a health hazard as using that method without knowing what i'm doing this amount of times is becoming a stressful mix. i would be greatful for anyone who can help!!