That gap is happening in your blog because the images are in separate paragraphs. You can remove that gap using CSS, but it will also removing spacing between paragraphs if you ever add several paragraphs of text in the future. Looking at your blog, that might be fine for you if you will always be posting images. You'll want to be careful with a change like this though and remember what you did if you add text paragraphs in the future:
#core-content p {
margin-bottom: 0;
}
Another option would be to add the images in a gallery or add them all in a row in one giant paragraph and then float them left if needed.
Try out a single column full width gallery to see if you like the way it looks:
[gallery columns="1" size="large"]
http://en.support.wordpress.com/images/gallery/