Only moderators or higher can upload images from their computers now. That is why you can post images and normal users cannot.
Oh If you guys want another way to post photos I know a trick xD First step take a photo or gyazo and click on the photo on the web page and hit "Copy link location or Copy image location " then come and post the link into <- that button.
You can follow Grace's method There's also another way, use picture applicants, such as Gyazo or Imgur. Just take the photo, and paste the link on your new thread or comment/reply.