You can try searching for "Kaveri River Tamil Nadu photos" or "Tamil Nadu Kaveri River images" on Google. You can filter the results to show only images by clicking on the "Images" tab. You can also use the "Tools" option to filter by size, color, and type.
The official Tamil Nadu Tourism website (tamilnadutourism.org) may also have a photo gallery section where you can find images of the Kaveri River and other tourist attractions in Tamil Nadu.