DrawingContext draw many images to one look crazy.

.NET framework 4.0

I draw many images to one, with some text.

One of image I draw is like this http://ww2.sinaimg.cn/bmiddle/9d8e3bd4jw1e45bz0upjvj20c8rt2b2b.jpg

We can see on the top part ,the image draw well, but on the bottom , we can't see the content of those images.

How should I do to make the draw work well ?

Thanks.