Hi Peter, your simple but great idea works fantastically! Thank you very much!
Anyhow you can combine pic02 and pic03
{\vbox{\externalfigure[pic02.jpg][scale=1000] \blank[whatever is needed] \externalfigure[pic03.jpg][scale=1000]}} {Caption}
and use two [2*1] combinations.
Just a fast example with \framed instead of \externalfigure
% - - - - - - - - \setupoutput[pdftex]
\starttext
\def\Double{\vbox{\framed[width=0.3\textwidth,height=.14\textheight]{} \blank[.02\textheight] \framed[width=0.3\textwidth,height=.14\textheight]{}}}
\startcombination[2*1] {\framed[width=0.6\textwidth,height=.3\textheight]{}}{1} {{\Double}}{2 and 3} \stopcombination
\blank
\startcombination[2*1] {\framed[width=0.45\textwidth,height=.2\textheight]{}}{4} {\framed[width=0.45\textwidth,height=.2\textheight]{}}{5} \stopcombination
\stoptext