Displaying a large bitmap file on a dialog box, in its original size, is quite difficult in the VC++ environment. However, it is possible to display a large bitmap to a predefined area of the dialog by using the StretchBlt( ) function.The major disadvantage of this is that the clarity of the image will be lost. Check out this article for displaying large bitmaps into the desired area of your dialog box in its original size with a scrolling technique used to show the entire bitmap.
滚动显示位图
在VC++环境下，在一个对话框中显示一个原始尺寸的大小的位图文件相当是困难的。然而,通过使用 StretchBlt()函数一个给定的区域显示一个大的位图是可能的。主要的缺点是图像将会失真。看了这篇通过卷动技术显示整个位图技术的文章，你将能够以它的原始尺寸在给定对话框的区域内显示一个大位图。
来源: http://www.codeguru.com/bitmap/ScrollBitmap.html