Manipulate bitmaps images in C++

I need to segment a scanned page to character zones.... something like identify the layouts of the page into text box and pictures.
The input of my program is a scanned page saved in bitmap format using a scanner, and my output must be a bitmap file of boxes
to show the text boxes.

In this lab, there is a bonus part for seperating the text boxes into lines.

I am quite new to bitmap processing, and I will be programming in C++ under UNIX.
Please help me if you know how do I decipher a bitmap?
How do we actually open a bitmap in the 1st place?
I have never open any file except ASCII files

Thanks

Example code in MFC for opening a Bitmap file.

BOOL CDib::ReadDib(const char* imageFile)
{
DWORD nBytes;
HANDLE hFile;
DWORD DibSize;

//----------------------
// Open the bitmap file.
//----------------------
hFile = CreateFile(imageFile, GENERIC_READ, FILE_SHARE_READ, NULL,
OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

if (hFile == INVALID_HANDLE_VALUE)
{
char errstr[100];

wsprintf(errstr, "Error opening file %s.", imageFile);
AfxMessageBox(errstr);
return FALSE;
}

//----------------------------
// Get the bitmap file header.
//----------------------------
ReadFile(hFile, &m_Bmfh, sizeof(BITMAPFILEHEADER), &nBytes, NULL);

//--------------------------------------
// If the header was not read completely
//--------------------------------------
if (nBytes != sizeof(BITMAPFILEHEADER))
{
AfxMessageBox("Could not read BITMAPFILEHEADER from file.");
CloseHandle(hFile);
return FALSE;
}

//----------------------------------------
// If the file type does indicate a bitmap
//----------------------------------------
if (m_Bmfh.bfType != * (WORD *) "BM")
{
AfxMessageBox("File type does not indicate BM.");
CloseHandle(hFile);
return FALSE;
}

//----------------------------------------
// Get the device-independent bitmap size.
//----------------------------------------
DibSize = m_Bmfh.bfSize - sizeof(BITMAPFILEHEADER);

//----------------------------------------------------------------
// Allocate memory to hold the complete device-independent bitmap.
//----------------------------------------------------------------
m_pData = new BYTE[DibSize + sizeof(BITMAPFILEHEADER)];

//---------------------------
// If error allocating memory
//---------------------------
if (!m_pData)
{
AfxMessageBox("Error allocating memory for bitmap.");
CloseHandle(hFile);
return FALSE;
}

//---------------------------------------------
// Copy the bitmap file header into the memory.
//---------------------------------------------
CopyMemory(m_pData, &m_Bmfh, sizeof(BITMAPFILEHEADER));
m_pBmfh = (BITMAPFILEHEADER*) m_pData;

//-----------------------------------------------------------------
// Read the remaining bitmap data following the bitmap file header.
//-----------------------------------------------------------------
ReadFile(hFile, &m_pData[sizeof(BITMAPFILEHEADER)], DibSize, &nBytes, NULL);

CloseHandle(hFile);

//-----------------------------------
// If error reading all of the bitmap
//-----------------------------------
if (nBytes != DibSize)
{
AfxMessageBox("Error reading DIB.");
return FALSE;
}

//-------------------------------------------
// Set the address of the bitmap info header.
//-------------------------------------------
m_pBmih = (BITMAPINFOHEADER*) &m_pData[sizeof(BITMAPFILEHEADER)];

//------------------------
// Verify the header size.
//------------------------
if (m_pBmih->biSize < 12 || (m_pBmih->biSize > 12 && m_pBmih->biSize < 16))
{
AfxMessageBox("Invalid DIB info header size.");
return FALSE;
}

return TRUE;
}

Hope this helps.
Regards,
Abadon