I forgot to include a MWE:

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\starttext

\setupexternalfigures[location={local, default}]

\startcombination[1*3]

{\externalfigure[cow][height=1cm]} {d}

{\externalfigure[cow][height=1cm]} {e}

{\externalfigure[cow][height=1cm]} {f}

\stopcombination

\stoptext

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Andres