An ISO or disk image is a file that contains an exact copy of a physical disk's structure and data. You cannot search its contents like a regular file because it's essentially a container holding an entire file system. To search inside it, you must first access its contents, typically by mounting it as a virtual drive or extracting its files using appropriate software.

The most common method is using your operating system's native capabilities: On Windows, you can double-click an ISO file to mount it as a new drive letter, then search the virtual drive using File Explorer. On Linux/macOS, use the mount command or graphical utilities. Alternatively, tools like 7-Zip or WinRAR can open the image and extract specific files for searching, which is useful if mounting isn't possible or desired. Disk imaging/forensic software offers advanced search within mounted or loaded images.

Searching via mounting offers immediate, non-destructive access, mimicking the original disk's behavior efficiently. The main limitation is the requirement to mount or extract the image first; true real-time indexing of the unopened file isn't feasible. Using extraction avoids mounting but requires temporary files. Always ensure you have legitimate access permissions for the image's contents when performing searches.