Baseline grids are super helpful for web designers, allowing us to maintain vertical rhythm on our designs. Problem is that it's complex and a pain in the ass.
Here is an example of baseline including an image
Images must be sized in height to a mutliple of the font size value, which is 18px in this pen, and have a margin bottom of line height. Vertical align is also required.
This example uses basehold.it. A cool overlay guide for baseline work.