合并两张jpg图片为一张jpg图片，思路是先把两张图片jpg图片都转化成bmp图片，然后把两张bmp图片合并成一张bmp图片，然后是把这张bmp图片转化为jpg图片。

一。jpg，bmp互相转化
/*********************************
format:bmp转为jpg， format为image/jpeg,jpg转为bmp,format为image/bmp
strDst为最终转化结果的图片路径
strSrc为原来图片的路径
**********************************/
BOOL ConvertPic(const WCHAR *format, const CString &strDst, const CString &strSrc)
{
BOOL bConvert = false;
CLSID clsid;
int nRet = 0;
nRet = GetEncoderClsid(format,&clsid);  //得到CLSID
USES_CONVERSION;
if (nRet>=0)
{
  Image image(A2W(strSrc));
  image.Save(A2W(strDst),&clsid,NULL);
  bConvert = true;
}
return bConvert;
}
其中GetEncoderClsid函数如下：
/*****************************************************
返回值为-1表示失败，其他为成功
******************************************************/
int GetEncoderClsid(const WCHAR *format, CLSID *pClsid)
{
int nRet = -1;
ImageCodecInfo * pCodecInfo = NULL;
UINT nNum = 0,nSize = 0;
GetImageEncodersSize(&nNum,&nSize);
if (nSize<0)
{
  return nRet;
}
pCodecInfo = new ImageCodecInfo[nSize];
if (pCodecInfo==NULL)
{
  return nRet;
}
GetImageEncoders(nNum,nSize,pCodecInfo);
for (UINT i=0; i<nNum; i++)
{
  if (wcscmp(pCodecInfo[i].MimeType,format)==0)
  {
   *pClsid = pCodecInfo[i].Clsid;
   nRet = i;

   delete pCodecInfo;
   return nRet;
  }
  else
  {
   continue;
  }
}
delete pCodecInfo;
return nRet;
}
bmp转化为jpg
ConvertPic(L"image/jpeg","c:\\1.jpg","c:\\1.bmp")
jpg转化为bmp
ConvertPic(L"image/bmp","c:\\1.bmp","c:\\1.jpg")

二。bmp图片合并
BOOL CombinePic(const WCHAR *format, const CString &strDst, const CString &strPic1, \
               const CString &strPic2)
{
BOOL bCombine = false;
int nRet = 0;
CLSID clsid;
nRet = GetEncoderClsid(format,&clsid);
if (nRet>=0)
{
  USES_CONVERSION;
  Bitmap bmp1(A2W(strPic1));
  Bitmap bmp2(A2W(strPic2));
  
  int nWidth = 0, nHeight = 0;
  nWidth = bmp1.GetWidth();   //假设两图片大小同
  nHeight = bmp1.GetHeight();
  Bitmap bmpCombine(2*nWidth,nHeight);  //高不变，宽*2，水平合并
  Graphics * pG = NULL;
  pG = Graphics::FromImage(&bmpCombine);
  if (pG!=NULL)
  {
   pG->DrawImage(&bmp1,0,0);
   pG->DrawImage(&bmp2,nWidth,0);
   bmpCombine.Save(A2W(strDst),&clsid,NULL);
  }
}
return bCombine;
}
例子：
CombinePic(L"image/bmp","12.bmp","1.bmp","2.bmp");

有了上面的功能，其他的就没问题了