To count words (as opposed to letters), it is necessary to strip HTML tags, and this includes images.
See the screenshot below:
Anyway, I think you can use the post template feature to add the content and the images:
{content}
{image}
Or a gallery:
{content}
[gallery link=”file” columns=”3″ )
Also, see the answer here:can-posts-word-limit-not-full-content-better-excerpts.