Are you talking about size as in width and height or is size of pixels.
If you have seen really big images maybe they have used the save for web and reduced the quality of the image.
I always use save for web in Photoshop and generally stick to around 480 kb.My images are usually 1200 x 798.
If you want to send me an image that has been refused and I will look at it.
Send to
eddie@landscape-images.co.uk