I wanted to add a signature image to all of my posts that were of a personal nature- but I did not want a border around the small thumbnail image. I found a way to delete the border. This is nothing fancy but it helped get ride of unnecessary boxes that may not be good for your design or vision?

1) To edit the image, click on it in the post editor.

2) In the top left of the image editor, click on the Advanced Settings tab.

3) Near the bottom there is a box that says Border, simply enter the number zero (0).

And, you will not have a border around your image. You can also custom resize in these settings as well. I hope this helps somebody out there, because it changed my life!