You may do it differently but this is my method, in the Apple world. Also there is a short wait for some steps to happen.
Send pic from my iPhone to my email
On Mac open the email and right click on the pic
'Save Attachment'
Select a folder in 'Finder' 'Documents', give it a useful name and 'Save'
At this point it may be appropriate to modify the image
In Sawmill Creek open a new message and put the cursor where the image is wanted
Select the 'Insert Image' icon, fifth from right in the middle row
Click on 'From Computer' select 'Choose File' this opens Finder
Go to 'Documents' and select the file
Select 'Upload File'
Done
Dovetails 1.jpg