@gaiabee: Yes, your site og:image
looks fine. But now you have 2 images.
1. Form Yoast SEO: which is showing as below. You can change this image from “SEO => Social => Facebook”. There you can upload your Frontpage image, which will be for your header image and also default image.
<meta property="og:image" content="http://voicesoftheselves.com/wp-content/uploads/2016/02/MG_3640-200x300.jpg" />
2. You need to remove another og:image
from header. The following code:
<meta property="og:image" content="http://voicesoftheselves.com/wp-content/uploads/2016/02/FB_logo_centered2_200x200.jpg" />
Note: If you are trying to add this image http://voicesoftheselves.com/wp-content/uploads/2016/02/FB_logo_centered2_200x200.jpg as your Facebook image for Homepage, then just go to “SEO => Social => Facebook” and paste this image url in “Image URL:” and “Save Changes”