I am not aware of a way to do this in JMP directly. However, you can create a new column that has both images joined together and then use that as your label column.
Here is a simple example:
Names Default To Here( 1 );
dt = Open( "$SAMPLE_DATA/Big Class Families.jmp" );
dt << New Column( "together", expression );
For( i = 1, i <= N Rows( dt ), i++,
hlb = H List Box( dt:picture[i], dt:pet[i] );
dt:together[i] = hlb << get picture;
);
dt:picture << label( 0 );
dt:pet << label( 0 );
dt:together << label( 1 );
Graph Builder(
Size( 528, 456 ),
Show Control Panel( 0 ),
Variables( X( :weight ), Y( :height ) ),
Elements( Points( X, Y, Legend( 6 ) ), Smoother( X, Y, Legend( 7 ) ) )
);
Jim