Can You Have Veneers if Your Teeth Are Already Straight but You Just Want an Improvement? (photo)

Of course you can! Veneers are performed for many different reasons. Try whitening first. If you like the color a cosmetic dentist can slightly reshape them for you. If this does not satisfy your aesthetic expectations, then consider veneers. They should look much better than either of the pictures that you attached as they should look thin, natural, and as white as you would like. Good luck!

Absolutely.  Veneers can be used to accomplish a number of different improvements to a smile.  Your idea of collecting photos that depict "how I want my teeth" ,as you say, is very helpful.  Find a dentist with lots of experience with cosmetic smile makeovers and schedule a consult visit to share your expectations, show pictures and discuss if this is realistic for YOU.  An experienced dentist should be able to guide you through options after listening to your goals and looking at your teeth.  The ultimate goal should be natural-looking teeth that are in harmony with your face and coloring.  And obviously if you're only doing 4 teeth on top and bottom, the shade match is critical to maintain a natural appearance.

The key in your case is likely to be good communication. While I don't do it often, yours is a good case for esthetic imaging. Shortening teeth isn't reversible so you need to have it well planned...start with whitening of course.