You’re welcome on the tutorial for the boxed images…it’s a newer video (with better audio too) for the boxed images. Anyway, the extra space you see is a result of the poor quality WP editor. When it seens a new line or space between to lines, it thinks it’s a paragraph, so it adds or wraps the item in a paragraph tag. Annoying actually.
When you paste the code into the editor, look for this part:
Make sure it’s on one line as you see above. If that still keeps the paragraph spacing (which is actually a margin on the
tag, then you can always add some custom css to your theme like this:
.thumbnail p {
margin-bottom: 0;
}
Best to do that in a child theme or a plugin that lets you edit the theme css, for example, Jetpack has Edit CSS, but there are other plugins that do editing. Remember that changing any core files means you lose the modifications should you update the theme, hence why the other methods above are best.