With SYP, you can places locations on a map, and add to them an image, a caption, and a text. This allow for example, to present your holidays or travels pictures, to promote interesting places in your area, to show different places of a convention, or prepare a hunt game. So, SYP can have many different usages.
SYP is a web CMS. It means a system to install and update a website. To use it, you need first to get a web hosting service. It must support php5 and a database. You must then download SYP, uncompress it and send it to your website. Then, follow instructions in README.txt.
May be, but I prefer to have my photos on my own site. So, I can keep all my intellectual property rights (that's often not true when putting them on a big commercial site). This also allows me to be independent from big companies.
And last, I prefer using free software.
I known some people would prefer pictures to display near the marker or in another corner instead of bottom-right corner. So, it's possible for SYP administrator to decide this an a per-site basis. Theres is a setting available in settings file.
If you want to change icone used to display markers, you can replace
marker-selected.png is used for a selected marker (green diamond