The Joel on Software Discussion Group

Does anybody have any information on screen scraping windows applications? (there's no other access that I'm aware of to the contents) I need to capture small sections of the window and then OCR them, preferably using c# or VB. I'm trawling through MSDN but haven't found anything suitable yet.

I recall making a app that thumbnailed a desktop by finding the id of the root win (it might even have been 0) and then drawing it to an offscreen canvas.  Pure WIN32.  Can't remember the details, but that was win2000 so security couldn't have been an issue.  Maybe I was running as administrator though ;-)

GetDC(NULL) gives you a handle to the desktop DC. That's what screen grabbers (including the Print Screen key) do.

On the other hand, if it's a lot of text, I would use some kind of "spy" program to extract the byte data directly from the app's window.

Try Spy++ from Visual Studio to find out what kind of window it is -- a browser control, an edit control, a plain canvas drawn with DrawText, etc., and take it from there.

You can find code written in Purebasic for a screen magnifier here.  Look at the AcquireImage() procedure to see the API calls in action.
http://forums.purebasic.com/english/viewtopic.php?t=11548

The MS Documentation can be found here:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/gdi/bitmaps_87eb.asp

Are you sure that taking an image and OCR'ing is the best approach. Download the Accessible SDK from Microsoft http://www.microsoft.com/enable/ and use their sample AccExplorer32 to see if it can extract the data. If it can, the Accessible API are fairly simple to add to your own program.

In most cases, you can get text directly by using GetWindowText or sending the appropriate window messages.