Photolock has no effect on Search Engine Optimization (SEO). The app works like any other app installed on your website. The website content and attributes that are important for SEO are not changed or affected in any way by Photolock.
There is only one exception. If you turn on Google & Bing Lock, Photolock will send signals to these search engines telling not to index your images. While this signal has no effect on search results, your website will not appear in "Image search" within a couple of weeks of activating this lock but it will keep appearing on regular search results.