AT_ERRCOUNT ACCUAPI IG_REC_letters_set(
   HIG_REC_IMAGE hImage,
   LPAT_REC_LETTER pLetter,
   AT_INT Length
);

AT_ERRCOUNT ErrCount = 0;
HIGEAR higImage = 0;
HIG_REC_IMAGE higRecImage = 0;
LPAT_REC_LETTER pLetters = 0;
AT_INT nLetterCount = 0;
AT_INT nLetterIndex = 0;

ErrCount += IG_load_file("Image.tif", &higImage); 
ErrCount += IG_REC_image_import(higImage, &higRecImage);
ErrCount += IG_REC_image_recognize(higRecImage);
ErrCount += IG_REC_letters_get(higRecImage, &pLetters, &nLetterCount);

for (nLetterIndex = 0; nLetterIndex < nLetterCount; ++nLetterIndex)
{
    if (pLetters[nLetterIndex].Code == (AT_WCHAR)'A')
    {
        pLetters[nLetterIndex].Code = (AT_WCHAR)'Z';
    }
}

ErrCount += IG_REC_letters_set(higRecImage, pLetters, nLetterCount);
ErrCount += IG_REC_image_recognize(higRecImage);

//...

ErrCount += IG_REC_free(pLetters);
ErrCount += IG_REC_image_delete(higRecImage);
ErrCount += IG_image_delete(higImage);