Warhol was a leading exponent of the pop art movement that flourished in the 1960s, with images of Marilyn Monroe, Elizabeth Taylor and Campbell's soup cans among his most famous works.
Portrait Salon was formed last year and describes itself as a form of Salon des Refuses - an exhibition of works rejected from a juried art show - that aims to showcase the best of the rejected images from the Taylor Wessing Portrait Prize, which is organised annually by the National Portrait Gallery (NPG).