[city41]

If you are on desktop, when clicking the "I am human" checkbox, hold your mouse down for a few seconds, and move it around just a touch for good measure, before letting go. This is usually enough to convince the system you are human and it skips the image hunt.

[ryantgtg]

This is great. Do you have any more tips about how to be more human?

[swiley]

Be lazy when clicking the images. Mailboxes are parking meters.

[jtvjan]

Look if the site has an option to use the noscript recaptcha (you might be able to force it to appear by blocking scripts). That one's much easier: as long as you get it right it lets you through, and you always have to select three squares (none of that "keep clicking until there's no more matching" garbage).

[unixfox]

Unfortunately this is becoming fairly rare, I haven't encountered one in ages.

[julianlam]

The first set is all you really need. Answering the second set (if presented) with completely wrong answers will usually cause you to pass. Wild guess -- perhaps ReCAPTCHA is checking for mouse movement and other behavioural heuristics after the initial test.