To the right of the Chat text box, click on the picture icon below the emoticons icon. You will have 2 options: 1) Drag an image inside of the pop-up window. 2) Click “Choose a File”, go to the folder in your computer containing the image, select the file, click open, and it will be uploaded to the Chatroom as a message.
A second and faster method to use if you want to post charts from your trading platform is to use a screen capture software to capture your screen, and then copy and paste the image right into the text box area of the Chatroom (in Windows just press Control key and V in the chat box to paste your image).