VS 2010 Optimizing Merging Of An Image?

I'm having a speed issue with some drawing in a program I am working on. I have narrowed down the speed issues to a single function. The cost of this function is such that I really need to find a way to make it faster, and that should be possible.

The function is this:

Public Shared Sub SuperImposeFishAni(ByVal bckGrnd As Drawing.Bitmap, ByVal dtop As Integer, ByVal dleft As Integer, ByVal dwidth As Integer, ByVal dheight As Integer, ByVal ImageInQuestion As FishImages)
Dim tp As Integer = 0

[code]....

This is actually a holdover from an earlier design that included animation, but that's probably irrelevant. What is happening here is that a bitmap (bckGrnd) is passed to the method along with the left, top, width, and height that are to be drawn, and a single variable to select which image to draw.The image to draw is chosen in the select statement, which makes up the bulk of the method. The guts of the issue are the last few lines.

Through profiling, I was able to determine that if this method is called, the drawing takes over .25 seconds, whereas if this method is not called the same exact drawing takes less than .07 seconds. Therefore, I am getting a significant slowdown from this one method, which surprises me, as it is pretty straightforward. It pretty much has to be this method, too, because I can perform the same actions with or without this method being called. It is called if a Boolean is True, which is about as fast a test as can be performed. If the Boolean is False, this method is not called. The >3x difference in timing is with or without this method.

The point behind the method is that the image from the select statement has to be superimposed onto the background image, and the size of the area, as well as the location, that it gets superimposed onto is almost totally arbitrary, which is why the size and location has to passed to the method.Technically, choosing the bitmap to merge in (the select statement), could be avoided, but I doubt that is the issue.