How do we understand if caliper brakes can be installed on the frame? I have a hybrid bike and I am converting it to drop bars. 

My problem is, as I am going to install STI's, I need to change brake system as well. I am using V brake types, how can I understand if I can install caliper brake or not? 

1- V brake is mounted on holes on the frame, are caliper brakes' start-end distance(I mean the distance between those holes and the wheel touch point)  same with V brakes'? 

2- Or, since my bike's frame is wider than a normal road bike(and using wider tires), is the distance between the mount holes OK or too wide? 

This is the random v brake image http://bicycletutor.com/images/bike/v-brake-400x280.jpg I am asking about the horizontal and vertical distances here.

This is the most detailed image of my bike I can find http://www.sedabisiklet.com/images/products/3/622015171123_200.jpg, sorry I couldn't find any photos from behind or front, so I can't show you more details.

edit: Found some better pictures of my bike. Please check them.

back 
http://i.imgur.com/Hj0ccPg.png
seems there is a hole like you mentioned. Not designed for mudguard (middle one, rear holes are for mudguards) I think

front 
http://i.imgur.com/XccwDqP.png
there is a small hole there, under the cable
Caliper brakes attach differently to V brakes, they have one pivot bolt in the centre rather than one each side. In your first photo there's a bolt that is in the right place although it's there for a mudguard/fender not a brake:



A caliper brake actually needs a hole right through there, and has a long bolt that goes right through. On your bike there are two chainstays there, with a brake bridge across. The problem is that it might not be strong enough to take an effective brake, since it's probably designed just to hold a mudguard. It will look something like this:



At the front, your fork is probably drilled to take a caliper brake and that part will definitely be strong enough. If it's not drilled you can probably get away with drilling it.

One alternative is to use cable pull adapters, the most common model being "travel agent".

It's likely to be cheaper to sell that bike and buy another one that has drop bars, than to convert the bike you have. Even if you use second hand parts for most of it, the new extra parts you need will add up.