Nice flowers. I like the way you can see the texture of the petals in the pictures.
Images uploaded to the database are resized to 1000 pixels wide. Anything wider than that will be reduced. I think the max file size for uploads is 10MB or 20MB (1 file at a time). I am never anywhere close to that (my pics are usually 2-3MB). If you resize to 1000 pixels you will get the fastest upload and maximum quality.
