image upload is required field, yet we're receiving entries with no images

Validation only checks to see that there is a field value, it doesn't go as far as checking to see that the upload process was complete. It checks to make sure that when the form was submitted that a filename existed in the file/image upload field.

If a user doesn't allow the file upload process to complete, browses away from the page, is disconnected, or any number of reasons why the upload did not complete... the field is still going to validate.

So what this means is if the field is required and they don't select a file and submit the form, it will return an error and ask them to upload a file.

If they select a file to upload, submit the form and the upload is disrupted for whatever reason, the form submission itself is still going to go through.

Validation occurs as a separate process from the actual upload. Validation simply checks for a value (or value formatting) at the time the form is submitted.