How to add an image with alt tag but without caption in Pandoc?

As described in the manual, in Pandoc’s Markdown images are added by

![This is the caption](/url/of/image.png)

The string This is the caption is added as a caption to the image as well as in the alt tag of the image.

I need the alt tags of the images, but want to avoid the captions for some of the images in an epub document. Is there an easy way to accomplish this, e.g. by css?