If you are looking for a way to use Photoshop on an older system like Mac OS X 10.4.11, The Status of Photoshop CS3 Downloads
For a brief period, Adobe provided a special version of CS3 that did not require activation for existing customers. However, those download links and replacement serial numbers have also been removed from Adobe's site. free download adobe photoshop cs3 for mac os x 10411 97 link
Adobe shut down the activation servers for CS3 years ago. This means that even if you have original installation discs, the software may not be able to "call home" to verify its license, rendering it unusable on new installations. If you are looking for a way to