This is something your WordPress theme or another plugin is adding to the image tags in HTML.
Some themes are developed with the ability to catch and modify page content before being delivered to a user’s browser.
Some of these themes try to go above-and-beyond by trying to make sure that the page content looks pretty. It does this by automatically adding line-breaks in HTML markup when it runs into certain characters.
The solution for this is to look for a setting in the theme to turn this off. If there is not a setting, you will need to contact the theme’s author and ask how to turn this off.