Craft
Photographs and drawings
A photograph shows what a thing looked like on one particular day. A drawing shows what a thing is. Catalogues need both, for different jobs.
The assumption that photography superseded illustration in catalogues does not survive contact with the catalogues themselves. Line drawings persisted in trade and parts catalogues for as long as those catalogues were printed, and they persisted for reasons that have nothing to do with cost or nostalgia.
Drawings suppress the accidental
A photograph records everything in front of the lens: a reflection, a shadow, a fingerprint, the particular finish of the one unit that happened to be photographed. Most of that information is irrelevant to the decision the reader is making, and some of it is actively misleading. A drawing includes only what the draughtsman decided mattered, which is exactly the right property when the reader needs to see a thread form or a mounting hole.
Drawings can show the impossible view
An exploded assembly, a cutaway, a section through a wall, a component drawn separately at twice the scale of the whole: none of these can be photographed, and all of them are routinely necessary. The moment a catalogue has to explain how parts relate rather than what they look like, illustration stops being an alternative to photography and becomes the only option.
Where photography wins
Photography is better wherever appearance is the product: texture, colour, drape, finish, the way a material catches light. A drawing of a fabric tells the reader nothing useful. Photography also carries a credibility that drawing cannot, because a reader knows a drawing was decided and a photograph was, at minimum, taken of something that existed.
Consistency matters more than quality
Whichever is chosen, the comparative function of the page demands that images of comparable items be made comparable: the same angle, the same relative scale, the same lighting or the same line weight. A row where one item is shot from the front and its neighbour from three quarters is harder to use than a row of mediocre but consistent pictures. Scale is the most frequently broken rule, and printing a scale reference or a stated dimension in the caption is the cheapest possible fix.
Captions are part of the picture
An uncaptioned catalogue image asks the reader to infer what they are looking at. A caption that names the view, the variant shown and any part not included resolves most of the ambiguity for a few words. The phrase noting that an accessory is shown but not supplied is worn out from use precisely because it prevents a genuine and expensive misunderstanding.