Mind the size
I just wanted to share a personal observation with the rest of the contributors. Maybe a lot of you are already aware of this but I guess some of you are not. So, it's about the maximum size we should save our images/illustrations. The thing is that if you upload images with resolution higher than 30 megapixels they won't be converted to TIFF format and you won't get the extra credits for the TIFF size in case of sale. This applies most to illustrations, collages and panoramas as these types of images are usually the largest in size.
Photo credits: Grigor Atanasov.