Google Ranking Factor – Image placement
The placement of images is far lass of an issue compared to the text placement factor, because images don’t convey much data for SEO.
These are generally limited to the image file name, title and ALT text, though some images may also have extended meta data such as licenses, image source information, artist or photographer, etc.
Any data rich images that are placed solely for their data may be penalized. I doubt this happens very often. What may happen is the use of pixel images – basically a single pixel that is invisible to the user, but carries data and may be placed for SEO or other reasons. The rule would be simple: the image must be visible and of a big enough size that it ads to the user experience.