The usual way to add an image to your posting is to select the tree symbol (insert/edit image) on the menu or if the image is in your LITF photo file then the option to its right - Content Selector. However a picture can sometimes be added directly from a web-site to a posting by right clicking on the image and then simply copy and pasting it into the blog.

If you do use the content selector then  make sure that you select the image size that you want to display.

Also if you copy and paste be careful as this does not always upload the picture. I think there are certain file types that it does not like!!