As far as DVDs are concerned, you can very often adjust the aspect ratio of the display (using the zapper) so that the it will nicely fit the screen. A bit of trial-and-error should do it. Some TVs even have an automatic fill-the-screen function but, in my experience, they aren't always very effective.
As far as still pikkies are concerned, it's only a potential problem, and then only if you leave one or more 'letterbox format' images displayed for a long time.
But if you have a wish to display pikkies regularly, then it's worthwhile pre-processing the source images to properly fill the screen and, at the same time, fix sundry other probs. If that's something you wish to do, let me know and we'll go into more detail. It can make a huge difference to still image display quality.