what is this load center amperage total?
In a case like this the easiest way to gauge service size is simply looking at the main breaker. Keep in mind, every part of the service; riser, meter pan, entrance cable, etc...must be sized and rated for the service size. 

In this case it looks like a 200A service. What you have there is a 200A, 20/40 main breaker panel. 20 full size spaces that can all accept twin, or tandem, breakers.

Not sure what you mean by what amperage the service "has". You can tell the service size like I explained, and you can tell what the load is at one pin pint in time by using a clamp-on amp meter. 

You can tell what the calculated load is by doing a load calculation on your home, although this is not an accurate number of actual draw. Here is one example: http://www.nojolt.com/load_calculations.shtml
You can do a web search for lots of info on load calculations.

Bear in mind, adding up the breakers in the panel is a completely meaningless number and will NOT give any kind of assessment of load. It is not uncommon to see 600-800 amps worth of breakers in a 200A panel.