DigitalGlobe recently released this article which highlights the use, by the Associated Press, of high resolution imagery from DigitalGlobe’s WorldView-3 satellite to combat slavery on fishing ships. You can read various Associated Press stories on slavery here and a story that specifically involved DigitalGlobe imagery here. The imagery is used to not only spot suspicious behaviour, but also identify ships from their masts and other distinctive features.
DigitalGlobe correctly claims that it is currently the world leader in resolution for commercial satellite imagery. It is likely that some countries have spy satellites with better resolution. Although the article mentions WorldView-3, DigitalGlobe also has WorldView-4, which was launched late last year and has similar resolution. WorldView-4 only went into commercial use this month.
We have previously looked at Global Fishing Watch, which monitors fishing ship locations and uses that information to identify illegal fishing. Maybe they too could help identify behaviour indicative of slavery on fishing ships. Apparently fishing ships carrying slaves spend most of their time at sea and offload their catch to other ships rather than returning to port.