It's a quirk in the forum software.
The forum software is supposed to resize your pics and display them within your post as a "preview" thumbnail. Sometimes it does strange things and tries to display the preview in full size and as a result only shows part of the pic. As Bill said above, if you refresh the page, it should re-display the preview pics correctly.
The pics display correctly in a pop-up window if you click on the "preview" pic.