South African president Jacob Zuma's attempt to have The Spear banned received a set-back after a judge said a ban would be difficult to implement.

The Spear painting in which South African President Jacob Zuma's genitals are exposed continues to draw controversy.

The president and his ruling African National Congress party have turned to the South Gauteng High Court in Johannesburg to have the painting banned.

The ANC started legal proceedings against the Goodman Gallery over the work entitled The Spear by artist Brett Murray.

The party branded the painting "indecent" and called on "all South Africans" to join Zuma, his family and other supporters at the South Gauteng high court because "of the outrageous depiction of the president in the so-called art by Brett Murray and the Goodman Gallery."

But the president's move suffered a setback after judge casted doubt on the enforceability of such a ban.

"This image is already out there on the Internet," AFP quoted Judge Fayeeza Kathree-Setiloane.

If a permanent interdict was granted that forbade the display of the painting or copies of it, "how will this court monitor compliance?" t she asked.

Outside the court a few hundred people had gathered to support their president and the trial was broadcast on big screens. Police cordoned off the areas and riot police guarded the entrance.

Supporters of the ANC's move say that artist's depiction of Zuma is racist and a reflection of cliché constructed during colonialism. They have also described the work of art as constituting an insult against the head of state.

The Goodman Gallery closed indefinitely on May 22 after two men defaced the painting.