The short answer is . Adobe has never released Photoshop CS3 as a free product for the general public.

Have you seen “Photoshop CS3 v100 free” being offered online? Share your experience in the comments below — but please don’t post direct download links.

: A dedicated adjustment tool that replaced more complex manual methods. Auto-Align and Auto-Blend

Are the free CS3 Downloads still available? - Adobe Community

The vast majority of search results for "Photoshop CS3 100 free" lead to cracked versions. These are full copies of the software with either:

Adobe provides a free, browser-based version of Photoshop called (accessible via creativecloud.adobe.com). It includes layers, filters, text tools, and basic adjustments. It is 100% legal, safe, and requires no installation. It is not CS3, but it does 90% of what most users need.