How to combine 2 images (say side-by-side)?

There are times where we need to combine 2 images in a short time frame. While this does not necessarily require s/he to have graphic design background, it may still be a tedious work if the person has not done this before, s/he may need to consider the pixel dimension, pixel density, background colour, etc before the actual approach can be decided.

My following approach is quite straight forward and assuming that both image has the same background colour, and the software that I am using is Paint.Net (since it is free!).

If the 2 images are both in the same aspect ratio then:
1. Open the bigger picture in Paint.Net.
2. Size it down to make it same size as the 2nd picture use: Image > Resize "Check the Maintain aspect ratio box"
3. Open Image>Canvas Size, double up the width and Anchor Right "Uncheck the Maintain aspect ratio box"
4. Import the other picture, Layers>Import From File "by default the program will Align the second picture to the left".
5. File>Save As...

If the 2 images are in different aspect ratio then:
1. Open the one with the bigger height.
2. Size it down so that the height is same as the 2nd picture.
3. Open canvas size, anchor right, increase the width by adding the width of 2nd picture.
4. Import the 2nd picture.
5. File>Save As...