If you are talking about RGB images, which have all the same size and "add with little space" means to set them side by side with a black bar:
Img{1} = rand(100, 100, 3);
Img{2} = rand(100, 100, 3);
Img{3} = rand(100, 100, 3);
Img{4} = rand(100, 100, 3);
Img1to4 = cat(1, ...
cat(2, Img{1}, zeros(100, 10, 3), Img{2}), ...
zeros(10, 210, 3), ...
cat(2, Img{3}, zeros(100, 10, 3), Img{4}));
If you want something else, please take the time to explain the details.
