I have the following image that I want to detect: 
After running following command:
opencv_createsamples -img banana.png -bg bg.txt -info info/info.txt -pngoutput info -maxxangle 0.5 -maxyangle 0.5 -maxzangle 0.5 -num 1950
It creates the image:
As it can be seen there is a white background around banana. Does anybody knows how to remove it?