This is a fast tip...
If you want to see how your image looks when published on DT, do the following using Photoshop...
Open your photo (Illustration);
Change the resolution from 300DPI to 72DPI;
Resize your image to width 300 pixels for landscape images or the height to 350 pixels for portrait ones;
From the filter menu choose the sharpen -> sharpen;
From File menu go to Save for web, choose the jpg format with 85% quality.
Now you will see the image the way it will show on DT if it was accepted and with out the watermark of course :)