You can make one image partially transparent if you want to compare two images in either Word or Excel.
For example, imagine you want to compare this image:
with this one:
First change the colour of the second image so it’s more obvious which is which. Select the image and then go to the Picture Tools ribbon and select Color and choose a colour from the Recolor options.
Here I chose a green colour
Then make the white areas transparent. Select the image again and on the Picture Tools ribbon select Color > Set Transparent Color.
The cursor will change to a pen symbol. Click on a white area of the image to make that area transparent.
If you are doing this in Word you need to change the wrap text settings before you can overlay the two images. Select the second (green) image and on the Picture Tools ribbon select Wrap Text > In Front of Text. You can then drag it into position over the first image.