RPC XML – Post with image on it NO Thumbnail !!!

Hi,

adding a wordpress post with a picture form the wp-admin work great and the picture is showing in the homepage as a thumbnail

But if i post with rpc xml with the balise <img class=”alignnone size-full wp-image-60″ title=”img” src=”https://my_blog.com/wp-content/uploads/my_picture.jpg&#8221; alt=”img” width=”304″ height=”171″ /> the picture is showing in the post but not in the thumbnail at the home page

i hope you got what i mean, and waiting for any suggestion