Removing the gray frame around inserted media

Hi – I’m trying to subtlety insert my logo at the end of my posts, but due to the logo having a white backdrop, the gray frame around the inserted media looks tacky and forced (scroll to the bottom of the following post: https://live432.com/2013/07/25/the-retirement-account-sunshine-without-my-face/). Is there any way to remove the WordPress gray frame?

Thanks for the help.