[colejohnson66]

The purpose of APIs it to provide a “uniform” interface. HTML layouts can change. JavaScript could be added to download the images after page load. An API shouldn’t change as often. And if the API is “versioned”, you can usually use the old version (old HTML layout) for a while before you upgrade (compared to your tool breaking as soon as the HTML changes).

[dreamcompiler]

The purpose of an API is like a company mission statement: There's one version written on the wall and then there's the actual version everybody knows is true but they don't say it out loud.

You described the written one above. GP described the actual one.

[account42]

That is the promise of APIs, but there is no guarantee.

[mrmonkeyman]

In theory, yes. In practice, no.