When viewing a page with a Slideshow block on it, I was seeing a tiny horizontal line (like a hyphen) appearing to the left of the image, near the top corner. I use Chrome for most browsing.

A tiny thing, but it annoyed me no end. It turned out to be a little piece of underlining for the <a> tag that encloses the image being displayed. If anyone else is similarly irritated by this, it can be fixed. Find and edit the file view.css in concrete/blocks/slideshow and add the following line to it:

.ccm-SlideshowBlock-display .slideImgWrap a {text-decoration:none; }

No more annoying little lines.