Assuming you're referring to images in notes, Zotero 5 didn't support images in notes at all — the fact that it worked at all was a fluke, and it broke syncing and caused performance problems.
Zotero 6 officially supports images in notes — you can drag them in or paste them from certain web browsers. It's not currently possible to paste in images from all local programs but we'll try to improve that in the future.
@LingT: We've restored the ability to paste images into notes on Windows in the latest Zotero beta, and if there are no problems it will be included in 6.0.5 soon. If you try the beta, let us know if you run into any trouble.
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Zotero 6 officially supports images in notes — you can drag them in or paste them from certain web browsers. It's not currently possible to paste in images from all local programs but we'll try to improve that in the future.