How to paint my acoustic guitar?
The second example ("No me llores") looks airbrushed to me. The first... frankly, I think that you could achieve it with nothing more than a wood stain, correcting fluid and a pocket-knife.

You should be aware, however, that both paintjobs are likely to impair the tone of the instrument. The first one, especially, looks like a number of no-skill, homebrew paintjobs that I've seen over the years. They do very little for a guitar as guitar.

The tone of an acoustic guitar depends greatly on how the soundbox vibrates. Applying a ham-fisted paintjob onto the soundboard, especially, will change its sonic characteristics. What is worse, heavy-handed painting will make it nigh impossible to repair the damage, once it is done (you might simply find it impossible to be rid of the paint without having to sand off a whole layer of wood that it has seeped into, which introduces its own set of problems). This is the reason acoustic guitars are given only a thin coat of soft paint.

I would not recommend doing anything like this to anything other than a cheap and already sub-par guitar - unless you have no intention of ever playing it.

Solid-body electric guitars are much more amenable to crazy paintjobs.