It is required that contributors assign one of the three illustration categories to their submissions that are not photographs. Even if you do not select any additional categories, selecting the one Illustration category is a must. Why is this so important? Because if you are familiar with our search options, there is a tick to select only illustrations or to entirely leave them out of the results. If you assign the correct category for yourself, the proper options are already preselected in the back-end (ie the review area), and the image is assured to be included in the relevant results. Of course, the editors have the ability to assign or re-assign the categories if they are misplaced, but this is additional work that should really be done by the uploader...
Moving on to the differences of the illustration categories. As said above, there are three:
1) 3D & Computer generated
2) Hand drawn and artistic
Although this seems logical and easy, I frequently see these three categories mixed and matched inappropriately. The first one is for all 3D artwork (abstract or otherwise) and all mathematically generated patterns and backgrounds. This includes various solely filter-based images created in Photoshop (KPT, fractals, rendered textures). This is, by far, the most crowded of the Illustration categories. Be very selective, when you wish to upload images here. I know that it is possible to create virtually infinite number of variations of the backgrounds rendered with KPT filters alone, but this does not mean they are distinctive of the other similar images on line. If you search for _abstract digital background_ (select only illustrations) and sort by downloads descending, you'll see that only a handful out of the sheer volume of such images have actual downloads. Most popular of those abstracts are still closely connected to a theme - like Christmas or winter...
The third is the most general of the three, this includes all other forms and fields of non-photography. If you cannot place the image in the above two categories, then assign this one. This includes general vector artwork solely produced with the aid of a computer (ie shapes and lines drawn originally on the screen, not scanned from other media). Themes included into this category consist of but are not limited to floral borders, illustrator/corel designs, non uniform backgrounds, clip-art, etc.
In a word - when uploading anything other than photographs, first select one or more of the appropriate Illustration categories and then fill in the remainder with other suitable categories. This helps the Editors in a big way and speeds up the process with fewer errors and more consistent search results for the buyers...