Imagemagick is a complex tool with a lot of options.
In the example you posted it seems that to the first image is superimposed (overlapped) a copy flipped with some transparency level. All actions that you can do at the price of a complicate commandline.
Let's suppose, for sake of simplicity, that you have just ready the two images. Give it a look to [1],[2] to understand better how it works. In the second reference [2] you can have a guess by examples about the methods available in Imagemagick to add two images.
Probably the -dissolve [3] or the -blend [4] option is what you are searching for:
composite -dissolve 50 -gravity Center a.jpg b.jpg -alpha Set result.jpg Another way to do it can be [5]
convert FUfstEv.jpg \ \( ChYNTch.jpg -alpha set -channel a -evaluate set 50% +channel \) \ -gravity center -compose over -composite result1.jpg Additional operation may have to be added to scale the image if needed... As additional reference you can see [n]. See again this page [5] for some examples.
In general the syntax of the dissolve option can be similar to the following one:
composite -dissolve -gravity Center \
1.gif 2.gif -alpha Set