The biggest single challenge in managing large quantities of images is that of categorization. Most photographers who accumulate more than a few thousand images are eventually obliged to confront the difficult issue of describing each one in simple terms so that it can be slotted into a practical and convenient retrieval system.

The key problem that must be resolved is how to divide work into readily understood categories and sub-categories so that electronic database systems can be used to quickly search and retrieve selections of images. The system used is inevitably dependent to some extent upon the type of work undertaken by a particular photographer. Clearly it is not necessary to maintain a wildlife category if no work of this type is undertaken. Nevertheless, it is possible to devise various categorization and cataloguing systems which have the potential to cope with images of more or less any type. Whatever system is used, it must of course evolve as a photographer's work develops and changes. Once broad categories have been decided, suitable sub-categories can be introduced, and these can then be further divided. Three levels of categorization should be sufficient for most applications.

One such system uses four broad categories at the top level. These are:

• the natural world;
• the human world;
• the works of mankind; and
• special interests.

these top-level categories can then be subdivided into:

• the natural world - landscapes, seascapes, the living world, the universe etc;
• the human world - portraits, family, candid, rural life, entertainment, nightlife etc;
• the works of mankind - art, structures, cities, food, industry, agriculture etc; and
• special interests - title images, lectures notes, drawings etc.

Finally, these sub-categories can be further divided into more specific subjects such as:

• the living world - mammals, reptiles, plants, insect, fish, arachnids, etc; and
• portraits - female, male, children, indoor, outdoor, studio etc.

Images can then be logically and consistently allocated locations or labels in a retrieval system using categories such as:

• the natural world / the living world / mammals; or
• the human world / portraits / children.

Every image should be labelled with an unique number, the subject it portrays, the location and the date on which it was taken. Without this basic information it is virtually impossible to publish or sell images.