So I know that the correct way of identifying pages in a sitemap is like this:
<url> <loc>http://www.example.com/</loc> </url>
If I want to include images in the sitemap, I know that I need to include the image extension and I could then include images like this:
<url> <loc>http://www.example.com/</loc> <image:image> <image:loc>http://example.com/image.jpg</image:loc> </image:image> </url>
My question is, what if I'm using a software that generates the sitemap without an image extension and instead adds images like this:
<url> <loc>http://www.example.com/image.jpg</loc> </url>
I know that Google is ignoring those images (at least it is ignoring them in webmaster) but could this have any negative affect on the functionality of the sitemap.xml file? I know that Google will ignore all canonical tags of a website if there are too many that point to deceptive or error pages — does this same concept apply to sitemaps that have URLs that are not pointing to indexable webpages? Is any documentation on something like this?
As per my experience it will not have any negative effect upon SEO. However, you must create a separate sitemap for your image collection which will works better in terms of search engine algorithms. That way, Googlebot will find the already segregated data (Page, Image, Post etc) for their crawling perspective.
For example you should go through Yoast plugin sitemap structure.
PFA screen-shot here. About what i am talking? Image sitemaps