To use Cisco IOS images in GNS3, you must typically provide your own image files because they are proprietary and copyrighted by Cisco. While GNS3 does not provide these images for free, there are several legal ways to obtain them for your labs.
If you or your employer has an active Cisco Service Contract , you can download certain images directly from the Cisco Software Central portal. Note that most older hardware images have reached "End of Support" and were removed, leaving the c7200 as one of the few remaining options.
The safest, most reliable, and legal method to get IOS images is by extracting them from physical Cisco hardware you already own.