使用after：pseudo-element插入的图像居中;不能使用跨度

I'm pulling in a tumblr feed using tumblr's code, and using after: to add an image as a separator between posts. I'd like to center the image, but haven't had luck doing so. Since tumblr's generating the content, not me, I don't think I can use span tags, which seems to be the usual answer. Any other ideas?I'm pulling in a tumblr feed using tumblr's cod