Hi Phil,
Go to your webshots page for this picture, look for 'other sizes' on the right and click it. Select the 425 size and when the code has been generated select everything in the 'direct link to image' box and copy it.
When you are creating yur post , use the Image button above the text box, paste the code into the box provided (overwriting the http:// that's in there), click ok and add a description, then click ok again.
Hope this helps
Best wishes
Barry