I must congratulate you, this tutorial is most useful! Great job!
I have 2 questions though:

1.) When my users upload images, they come on the bottom of the website. What do I need to do for new images to come on top of the previously published images?

2.) I know this is probably foolish question (new to websites'n'codes) but how can I put a restrict on uploaded images, lets say that their width must be less than 600 and height less than 500 for them to be uploaded? Can you write the code for this? I would be most grateful.