Just noticed that if the images contained in the post are not uploaded to connect, the preview image is replaced by the placeholder.
Please, implement the image parsing so that also external images could be used for preview (I use external images since 2017 november due to the 1000 photos limit).
Example:
This is from the share your photos and discoveries board: https://www.localguidesconnect.com/t5/Share-Your-Photos-and/bd-p/Photos