Alternatively, if you right-click on an image in Obsidian, you can “Show in system explorer”, and from there you can copy or drag the image directly from your file system.
If the image is a URL link instead of an attachment, you can copy the URL, and then paste the URL in Notion. You then have an option in Notion to “Embed image” and it changes the link to an image.
There is also an existing feature request to be able to copy images: Copy image from a note
Near the bottom of that thread is some discussion about plugins which may enable this feature. (I haven’t looked or tried.)