How are you sending? what your message body (request) looks like, what is your content type and how they're appearing at recipient end?
– HungryCoderMay 17 '17 at 14:23
Here's a link to the documentation for [inline images](https://developers.sparkpost.com/api/transmissions.html#header-inline-image-attributes). Seeing an example of what you're sending would help.
– Dave GrayMay 17 '17 at 16:26