/guides/frequently-asked-questions/forum-user-guide To insert a picture that is on your own computer:
Position your cursor where you want to insert the image in your post, and click the Image button (resembles a couple of mountain peaks).
Click "Browse Server", and then "Upload" in the top left of the new window that appears. Selecting "Choose File" will open a file explorer window where you can choose the image file that you want to upload and click "open".
Click "upload" and after a few seconds your picture will be uploaded to the server, and appear highlighted in your own folder. Click "Insert File" at the top of the window and the image will appear in an Image Properties window where you can chage the size if required, or simply click "OK" to add it to your post. The limitation is in the Drupal editor. We're using most stuff as it comes because it costs too much to customise.