The IMAGE command takes an MxNx3 matrix and displays it as an RGB image. You can use LOAD and RESHAPE to get the data into the right format. Finally, IMAGE wants either integers between 0 and 255 or doubles between 0 and 1.0, so you need to cast or rescale your numbers. The following code snippet should show you how to put it all together.
x = load('rgbdata.txt'); % makes a 12x3 matrix
x = reshape(x, 2, 6, 3); % reshape pulls columnwise, assume 6x2 image
x = x/255; %scale the data to be between 0 and 1
image(x);