The "label" option can be used for filtering for apparently any call that has multiple resulting rows.
index.php?module=API&method=ImageGraph.get&idSite=6&token_auth=anonymous&period=day&date=last100&apiModule=Actions&apiAction=getPageTitles &label=PageNameIWant
If you have many pages and you're getting a "No data for this graph" as result, possibly the page you're asking for is not one of the more popular. I'm not having this issue myself, but if someone in future does and reads this: there's a filter or filter_rows option which you can set to 0.