[Ffmpeg-user] About the watermark image

Hi all, I am new to ffmpeg, actually i want to put gif images into the video clip for that i am usingt this command : ffmpeg -i inputfile -vhook '/usr/lib/vhook/watermark.so -f cnn.gif -m 0 -t ffffff' -sameq output.mpg but after executing this command the image size is becomming larger ,I am unable to get the actual size for the image in the clip.The actual size of the gif image is 200x40 and i want to put that image to the bottom right hand side. For this i need some help regarding the parameters. So plz help me in this regard, and its urgent. praveen