good idea to get rid of the iplimages !
see, it gets much easier, too :
for(size_t i = 0; i < faces.size(); i++)
{
Mat roi(captureFrame, faces[i]);
std::stringstream sstm;
sstm << "faces\\" <<counter << ".jpg";
string result = sstm.str();
imwrite(result.c_str() , roi);
counter++;
}