If you have the pictures saved on your PC or laptop, simply click on the icon that looks like a mountain next to the smiley in the ribbon at the top of the text box. you will get a drop down box click on that and it will ask you to browse then simply go to the folder with your pictures double click on the picture required and it will appear in the text box.
I’m just asking for my own convenience I’m not overly fond of seeing thumbnails in a message that I then have to click, when putting the full images into the posts is much handier for the reader.