Several Ikea Ribba picture frames into one large picture

Hello,

I recently saw the following decoration at an Ikea.



How were the individual Ribba picture frames assembled?
I don't think hot glue is ideal for that.

Regards
Spiku

Could you see through it? I would initially assume that the frames are mounted on a carrier plate.

Unfortunately not, because the collage was directly attached to the wall.

I would agree with the IKEA expert. I think the shadows look like there is a gap to the wall and the frames are mounted again on an extra panel.