Always run certutil -hashfile file.iso SHA256 and compare against the community-provided hash.
The concept of a "highly compressed" Windows 7 ISO often refers to modified versions of the operating system that have been stripped of non-essential components to reduce file size—sometimes to as low as 100MB to 500MB—from the original 2.5GB+ windows 7 iso highly compressed
A clean Windows 7 SP1 x64 ISO is approximately 3.1GB . Always run certutil -hashfile file