Patent drawings have to be good enough to show and describe the invention as is necessary for a skilled artisan in the relevant industry to understand the invention when viewing the drawings together with the written description of the invention. There are few hard-and-fast rules on the quality of the drawing, though. Drawings must include black-and-white lines, and will generally be rejected where they include shading or color. In rare cases, color drawings may be necessary as the only practical medium by which to disclose the subject matter sought to be patented. But generally, drawing must be in black-and-white.
Drawings can be produced by hand or by computer. Photographs are not accepted except, again, in very limited situations where a photograph is the only practical medium for disclosing the subject matter, such as when describing cell growth, crystalline structures, electrophoresis gels, and other complicated illustrations. Instead, black and white line drawings are preferred in almost all situations.
Drawings used to be produced by hand. They were human and beautiful. Today, most drawings are done with CAD tools or other computer drawing programs. There is no requirement that the drawings be created by a computer, and no prohibition against hand-drawn drawings. Generally, as long as the drawings are clear and can be reproduced, they are acceptable.
All drawings must be made by a process which will give them satisfactory reproduction characteristics. Every line, number, and letter must be durable, clean, black (except for color drawings), sufficiently dense and dark, and uniformly thick and well-defined. The weight of all lines and letters must be heavy enough to permit adequate reproduction. This requirement applies to all lines however fine, to shading, and to lines representing cut surfaces in sectional views. Lines and strokes of different thicknesses may be used in the same drawing where different thicknesses have a different meaning.