95% of the people that responded to this question have given you the answer you need to upload image.
But if you still don't get it right, kindly Copy someone post with image and then edit it to upload your image.
Example; Go on bitcointalk, check someone post and click Quote to copy the HTML Code of the person. From there you will see the link to the users image, Delete the original link of the person by inserting your. When done copy the edited version to paste on your dashboard to upload.
That's how I learnt how to started posting image too