\setupexternalfigures[location=default]

\starttext

\bTABLE[frame=off,align=middle]
  \bTR
    \bTD 

		\placefigure[][fig:ref]{caption for two}{
		\startcombination[2*1]
		{\externalfigure[cow][width=0.25\textwidth]} {(a)}
		{\externalfigure[mill][width=0.25\textwidth]} {(b)}
		\stopcombination
		}
    \eTD
    \bTD \placefigure[][fig:ref2]{Caption for one}{\externalfigure[hacker][width=0.25\textwidth]} 
	\eTD
  \eTR
\eTABLE

\stoptext