How to attach figures, images of pictures side by side to make one new picture in ubuntu

Hi,
I have two images image1.png and image2.png.
I wanted to combine these two side by side to make a new image combimage.png.

I tried using gimp and photo editor in ubuntu to manually keep the images side by side and save it as a new image. But I couldn't. I found this really useful command in a blog.

montage -tile 2x1 -geometry +0+0 image1.png image2.png combimage.png
This combines the images image1.png and image2.png to 2 rows and 1 column.

montage -tile 1x2 -geometry +0+0 image1.png image2.png combimage.png
This combines the images image1.png and image2.png to 1 row and two columns.

njoy!