Stock is the expensive-looking free option
It costs page weight, communicates nothing specific, and places you visually alongside every competitor using the same library. It is chosen because the layout has a space, which is not a reason.
Real photography, if it is genuinely real
Your actual team, premises or work is specific and unrepeatable, and it does the same job as detail in a case study — it would be embarrassing to fake, so it is believed.
If the photograph could appear on a competitor’s site, it is doing nothing for you.
Illustration for concepts, if it is a system
A consistent illustration style can carry personality where photography can’t, but it only works applied uniformly. Mixed styles read as accidental, which is why it belongs in the design system rather than in a single page.
Diagrams earn their place most reliably
A drawing showing how something works communicates faster than paragraphs and is specific to you. Where the subject has structure, this is usually the highest-value image on the page.
Sometimes nothing is right
Strong typography and generous space can carry a page entirely, and the fastest image is the one you deleted — the argument behind a confident page rather than a decorated one.
Whatever you use, size it properly
Resize once to a small ladder of widths, serve static derivatives, set dimensions, and lazy-load only what is below the fold. Decoration that slows the first screen costs more than it adds.