GIMP (stands from GNU Image Manipulation Program) is an open source image and photo editing tool. In short, GIMP is the free and open-source alternative to Photoshop, available for almost all operating systems (Linux, Microsoft Windows, OS X).
According to this UN report, more people worldwide have mobile phones than toilets. I want to write an article about this report and I will blend two images to use the result as the article image.
I will use two public domain images. The first one shows men silhouettes using mobile phone photos:
Second image shows a ground toilete in Botswana:
From the Menu, select: File → Open as Layers…
Use CTRL + CLICK to select the images. The result is
Resize canvas and arrange images
From the Menu, select: Image → Canvas Size…
Using the Move Tool from the Toolbox window
Place second image to the right side of canvas
Add Layer Mask
From the Layers window, select the second image and Add Layer Mask
From the Toolbox window, select the Blend Tool
Click and drag the Blend Tool in the images overlap
The result is
This is the finally blending result:
Experimenting with different parameters can give even better results.