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Well, first of all you upload your images to a site like Flickr or Postimage, some now charge so be careful, unless you want to, of course! you'd probably get a better service? 
Then you use the address/link/pathway of the image, after you've uploaded it, & insert it in the box that appears when you click on the "insert an image" icon (above the asterisk, hopefully!) You can usually resize when you first upload the image or when you post it, in the width & height boxes that appear, usually a width of around 640ish.
As I'm typing I'm sure I remember this being covered before, I'll have to have a look!

edit: you have to reply directly to this post to see where the asterisk is!!! I can't find a copy of the "insert an image" icon!! sorry 

Malcolm did this a while back - https://www.ttwebsite.com/forums/showthr...?tid=18350