It already has what you are asking for... at least the most current version does v220.127.116.11.
1. On the history/settings window there is a toggle for copying to clipboard or not.
2. If you right click on the select area you will get a Copy to Clipboard menu item.
3. Once you have your annotated image you can open the history window and drag/drop the image onto that window and it will upload to imm.io.
Might want to read the help/website next time. LOL http://icup.pen.io/