KaraMarie -- I have many gorgeous invisible quilts, too.
I get my pictures to the best size by using the screenshot tool in the software. In microsoft it is a free program called Snip and Sketch. Capture your image in the snip and save it with a name to your desktop. In the thread click on the "go advanced" and find the "manage attachments" section. Upload your saved snip, scroll right to find the upload button and hit upload. When you submit your thread, the picture should be at the bottom of your message. Give it a shot! I want to see your quilt! Gotta love hexies!