Dynamic memory allocation and exception safety

Imagine that you have to write a program to rotate images. Your program takes the name of the file and the angle of rotation as input, reads the contents of the file, performs the processing, and returns the output. Here is some sample code.

 1 #include <istream>
 2 #include <fstream>
 3 typedef unsigned char byte;
 4 
 5 byte *rotateImage(std::string imgFile, double angle, 
 6                   size_t& sz) {
 7   // open the file for reading
 8   std::ifstream imgStrm(imgFile.c_str(), std::ios::binary);
 9 
10   if (imgStrm) {
11     // determine file size
12     imgStrm.seekg(0, std::ios::end);
13     sz = imgStrm.tellg();
14     imsStrm.seekg(0);        // seek back to start of stream
15
16     byte *img = new byte[sz]; // allocate buffer and read
17     // read the image contents
18     imgStrm.read(reinterpret_cast<char*>(img), sz);
19     // process it
20     byte *rotated = img_rotate(img, sz, angle);
21     //...