If you have that images available directly in HTML code, a sitemap for the images is not necessary.
As others have stated, a sitemap isn't necessary for such a small amount of content. If you really want to have one, then including everything on one sitemap is okay.
Can you combine an XML Sitemap with an Image XML Sitemap?
You can use a separate sitemap to list images, or you can add image information to an existing sitemap.
Can you combine an XML ...
If your site uses a lot of graphics that are central part of your business strategy, I'd recommend you use one.
If it's just a few images / videos, perhaps skip the use of sitemaps as Google will take care of it.
Here's an excerpt from https://support.google.com/webmasters/answer/178636?hl=en
Follow Webmaster Guidelines and best practices for ...