so you are here in the message box, just above there are a line of boxes:
click on the one that says 'host an image':
you will see a pop up appear:
click on choose file and a window will appear, go to the folder where the image is:
double click on the image, you will see the name of the file next to the button 'choose a file':
you now click on 'send'.
you will see another window:
right click on the image address:
copy and past in the message box:
you will see the picture address in the message box:
clicking on the preview button you will see how the post will be:
finish the message and send to post it...