How about trying to drag and drop the image onto the email page you are writing. Does that work?
I drag and drop all kinds of attachments to emails.
I predominantly use MacOSX so I can't remember if it's possible for Windows users. It might also depend on email service, some have the drag & drop ability & some do not.

Alternatively, if you click the attachment icon it will usually open an Open File menu to choose the file. If the icon is not showing up it might be due to it being hidden. Use the scroll bar at bottom of page or if all you see is a ... on menu then click on that ... for more options.