At this time it's not possible to review an attachment once it's been appended to an email message, aside from verifying the file name in the list of attachments.
I can see the value in adding this functionality. When you receive an email message, you can click on the image thumbnail to preview it before downloading, and I can see how it would be beneficial to click on image you've just uploaded to ensure it's the correct one. I'll change this thread to a Proposed Idea to facilitate tracking on this request. Other users can vote up the thread and add their input on its implementation. While this does not guarantee the functionality will be added, it does get it in front of our developers so they can see its popularity and usefulness.