I am using Monkeyrunner (automation) to test an app on an Android device (Samsung S2), and since it does not allow me to see image patterns on the screen, I have to rely on
To limit logcat output to messages which happened after certain moment you do not have to clear the log. Instead use logcat -T <timestamp> filter. Supported timestamp formats depend on the Android version - see -T paragraph in logcat -h output.