HTML is the preferred log type to access the screen snapshot.
Select HTML as the log type in the Logging Preferences Page in RFT Java or the Logging Options Page in RFT .Net.
After playback fails the log opens in your browser.
RootTestObject exposes a getScreenSnapshot method that will return a snapshot of the screen. GuiTestObject exposes the same method, but only captures the portion of the screen rendering the TestObject. LogInfo, LogError, and LogWarning all have overloads that will take a snapshot and add it to the log.