The different stats programs use different methods for calculating the numbers. Users will also notice that google analytics records different numbers too.
The website stats program "AWstats" filters out a lot of visits that it suspects are robots, and non-human traffic. Also the AWstats records views to all pages and items on your website.
The image views stats program only records image views - it doesn't record views to gallery pages, or blog pages etc.
The image view counts generally don't filter out non-human traffic, so they usually include visits from search engine spiders and other traffic that isn't necessarily a real person.
In short every stats program has a different method of recording stats and no method is 100% accurate.