First of all, you need to include include_entities=true as part of the request:
i.e. https://api.twitter.com/1/statuses/user_timeline.json?screen_name=twitter&include_entities=true
Then find any media_url elements; they will contain the url for any photos. It may contain video links, so you have to filter out common image types (.png / .jpg / .gif / etc).
See: Tweet Objects
Derek spinger
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