but many of these are stock images. that unless bought can't be used and usually not sold in this context... but in any case, you should post the image itself, not a camera phone copy of a print. that makes little sense.
i would suggest posting only your own personal work. i know people on some stock sites that will pounce on people selling their work as their own. only post the actual image and not a copy of one. in order to even print here the work has to look perfect up close. see that stock shot of that train? its totally blurry up close because it was enlarged about twice or so. everything else is slanted. even as a presentation of your work, it doesn't really work. for the artwork, scan that it. for actual photos, upgrade your phone or get a better camera. if your goal is to sell, your work has to be as good as the other stuff here - or better.
---Mike Savad
MikeSavad.com