Franco Vaccari, an Italian conceptual artist whose experiments with photography expanded the medium’s possibilities, has died at 89. His death was announced by his gallery, the Bologna-based P420, which did not specify a cause.

Vaccari died just four months before his work was due to be surveyed in a retrospective held at Museion in Bolzano, Italy. Opening in March, the exhibition was being staged to mark what would’ve been Vaccari’s 90th birthday and is due to explore how the artist brought his work beyond art spaces, into the eye of the general public.

He often relied on viewer participation for the completion of his pieces, which he typically called “esposizioni in tempo reale,” or “exhibitions in real time.” The most famous of them, a work called Esposizione in tempo reale n. 4. Lascia sulle pareti una traccia fotografica del tuo passaggio, figured in the 1972 Venice Biennale and was mostly composed of a photobooth known as a Photomatic. Vaccari sat for the first picture, then asked his viewers to follow suit and forfeit their picture, which then was exhibited for others to see.

Following the success of that piece, Vaccari produced Photomatic d’Italia (1972–74), for which he asked visitors to some...