You were close. You just have to paste the url of the image itself instead of the google images link.
On computer: Right click the image you wanna paste and select "Copy Image Address" and paste that in the post editor.
On a tablet/phone: Tap and hold on the image you wanna post and a menu should pop up. One of the items should be "Copy Image Address" or something similar. Tap that then paste it in the post editor.
Edit: What Kudasai posted also works.
The method differs depending on whether you're on a computer or phone/tablet, but all you usually have to do to post an image is post the url of the image itself. The post editor should take care of the rest.