Hi Richard,
we have very limited possibilites on localhost software. I hope you know why.
But check those:
- Are you able to upload .jpg, and .png files using Joomla native Media Manager?
- Are you able to upload those files using Joomla TinyMCE/JCE editor inside article?
- Enable Showing errors to Maximum + Turn On Debug mode in Joomla Global Configuration and check upload process again. Also check server error log from server.
My guess is that the problem lies with the localhost software settings. But we are not his software support to help you more.
In general it is strange, because in general people have a problem with .svg type files and not the files format, which has been around for more than 35 years, and it's fully supported by WAMP, MAMP and XAMPP.