Can I add a GIF to a blocks page?

From YourHead

Image blocks will convert all images to PNG, so you cannot use image blocks. However you can use GIFs that are dragged into a Text block. See above for a how-to.

A note about PNG images

Internet Explorer may be a very bad web browser, but it does command that vast majority of the market share of your potential viewers. So it's an important consideration. Many people (wrongly) believe that PNG is not useable in Internet Explorer. In fact a PNG image can be viewed with full alpha channel transparency in Internet Explorer, even on Windows. However care must be taken to run a special Windows-only behavior that asks Internet Explorer to post-process the image. Why isn't this more widely done or used? Because it's quite difficult. But Blocks does this automatically whenever you use PNG images. So don't worry, use PNG and transparency wherever you like. With Blocks all of your customers will see your great content.