I want to combine GIF images with Ruby

I just want to attach the GIF image, but I don't know how to do it.
When I looked it up, I could only find RMagick and MiniMagick that I needed.
The processing itself is simple, so if there is a way not to use ImageMagic, I would like to use it.
There is no problem using Gem without ImageMagic.

Here's what I'm trying to do:

+---+
| A|
+---+

  +

+---+
| B|
+---+

  ↓

+-------+
| AB|
+-------+

I would appreciate it if you could tell me the sample code and the site.
I look forward to your kind cooperation.