jpeg.dll - was is da drin?

#include <string.h>
#include <stdio.h>
#include <stdlib.h>
#include <windows.h>
#include <jpeglib.h>

HINSTANCE hInst;
int much=1;

LRESULT CALLBACK WndProc (HWND, UINT, WPARAM, LPARAM);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR CmdLine, int nCmdShow) {
 MSG msg;
 BOOL bRet;
 hInst=hInstance;
 HWND hWnd;
 int xwin=0;
 int ywin=0;

 char winclass[] = "Fensterklasse";
 WNDCLASS wc;

 wc.style = CS_HREDRAW | CS_VREDRAW;
 wc.lpfnWndProc = WndProc;
 wc.cbClsExtra = 0;
 wc.cbWndExtra = 0;
 wc.hInstance = hInstance;
 wc.hIcon = LoadIcon (NULL, IDI_APPLICATION);
 wc.hCursor = LoadCursor (NULL, IDC_ARROW);
 wc.hbrBackground = (HBRUSH) GetStockObject (BLACK_BRUSH);
 wc.lpszMenuName = NULL;
 wc.lpszClassName = winclass;

 RegisterClass (&wc);

 xwin=GetSystemMetrics(SM_CXSCREEN);
 ywin=GetSystemMetrics(SM_CYSCREEN);
 xwin /= 2;
 xwin -= 400; //800 Breit
 ywin /= 2;
 ywin -= 200; //400 Hoch

 hWnd = CreateWindow (winclass, "Hello World", WS_OVERLAPPEDWINDOW, xwin, ywin, 800, 400, NULL, NULL, hInstance, NULL);

 ShowWindow(hWnd, nCmdShow);
 UpdateWindow(hWnd);

 while( (bRet = GetMessage(&msg, NULL, 0, 0)) != 0) {
  TranslateMessage(&msg);
  DispatchMessage(&msg);
 }

 return msg.wParam;
}

LRESULT CALLBACK WndProc (HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam) {
 HDC hdc, hdcb;
 HBITMAP hbit;
 PAINTSTRUCT ps;
 RECT crect, wrect;
 int xdiff;
 int ydiff;
 int x, y, i;
 struct jpeg_decompress_struct cinfo;
 struct jpeg_error_mgr jerr;
 FILE *infile;
 byte *buffer;
 byte r, g, b;

 if (msg == WM_PAINT) {
  if (much==1) {
   much=2;
   GetWindowRect(hWnd,&wrect);
   GetClientRect(hWnd,&crect);
   xdiff=(wrect.right - wrect.left) - crect.right;
   ydiff=(wrect.bottom - wrect.top) - crect.bottom;
   wrect.left=wrect.left - (xdiff / 2);
   wrect.top=wrect.top - (ydiff / 2);
   xdiff += 800;
   ydiff += 400;
   MoveWindow(hWnd,wrect.left,wrect.top,xdiff,ydiff,TRUE);
   hdc=BeginPaint(hWnd,&ps);
   EndPaint(hWnd,&ps);
   InvalidateRect(hWnd,NULL,FALSE);
   return 0;
  } else if (much==2) {
   much=3;
   cinfo.err = jpeg_std_error(&jerr);
   jpeg_create_decompress(&cinfo);
   if ((infile=fopen("zb.jpg","rb")) == NULL) {
    MessageBox(hWnd,"Grafik konnte nicht geöffnet werden: zb.jpg","Error",MB_OK);
    PostQuitMessage(0);
    return 0;
   }
   jpeg_stdio_src(&cinfo, infile);
   jpeg_read_header(&cinfo, TRUE);
   jpeg_start_decompress(&cinfo);
   buffer = (byte*) malloc(2400);

   hdc=BeginPaint(hWnd,&ps);
   hdcb=CreateCompatibleDC(hdc);
   hbit=CreateCompatibleBitmap(hdc,800,400);
   SelectObject(hdcb,hbit);
   y=0;
   while(cinfo.output_scanline < cinfo.output_height) {
    jpeg_read_scanlines(&cinfo, (JSAMPARRAY) &buffer, 1);
    i=0;
    for(x=0; x < 800; x++) {
     r=buffer[i];
     g=buffer[i+1];
     b=buffer[i+2];
     i+=3;
     SetPixel(hdcb,x,y,RGB(r,g,b));
    }
    y++;
   }
   EndPaint(hWnd,&ps);
   jpeg_finish_decompress(&cinfo);
   jpeg_destroy_decompress(&cinfo);
   InvalidateRect(hWnd,NULL,FALSE);
   return 0;
  } else {
   hdc=BeginPaint(hWnd,&ps);
    BitBlt(hdc,0,0,800,400,hdcb,0,0,SRCCOPY);
    SelectObject(hdc,(HPEN) GetStockObject(WHITE_PEN));
    MoveToEx(hdc,50,50,NULL);
    LineTo(hdc,100,100);
    SetPixel(hdc,100,50,RGB(255,0,0));
   EndPaint(hWnd,&ps);
   return 0;
  }
 }
 if (msg == WM_DESTROY) {
  PostQuitMessage(0);
  return 0;
 }

 return DefWindowProc(hWnd,msg,wParam,lParam);
}