I don’t think Lemmy has Reddit-style crossposting. Your options are:

• Make a URL post that links to this post’s comment page as if seen via czech-lemmy.eu: https://czech-lemmy.eu/post/74235 – this option is closest to a Reddit crosspost but it is not recommended to use instance-specific links, though, and the image may not show up in the post thumbnail.

• Make a URL post with the image’s URL: https://i.imgur.com/Li9eTmZ.jpg – this does not preserve a link to this discussion but you can add [Original post](https://czech-lemmy.eu/post/74235) at !pics@lemmy.world in the post body or a comment

• Make an image post by reuploading the image. This is just option #2 but with the image rehosted at your home instance (lemmy.world).

I would personally choose option #2.