The bulletin board will pull in the first image from the post as the displayed image on the slider (it will scale the image to fit) If it is scaling in an image that is disproportionate then the slider image will be squashed or extended, for example the slider default image size will be 333 x 250 (landscape photo) so anything that is squared eg 400 x 400 will by default be resized to 333 x 250 in the slider and therefore 333 x 250 images will be preferred or images in that ratio.

The bulletin is set by default to pull in an exerpt from the post to display, so make sure that the exerpt is filled with part of the post when composing the bulletin (for example the exert is this entire post)

Lastly make sure that the Add this post/page to Smooth Slider is checked when posting the bulletin