I'm using Sleek Template Original.

As you can see... there is too much black space... the image size is 150x96 when I set it up in the plug in interface as 200x150.

What I'm doing wrong?

puntcastello.es/component/k2/item/5

If the images are all resized in 150px width then you should also put in the plugin this dimension. Is there a particular reason you have put 200px in the plugin?

The real image size is 600x480px... so when the pop-up image is clicked... this will be showed on this way.

In the plug in, the size informed is "thumbnail viewport width", if you let the "thumbnail sizes" in blank, the  plug fixed his own size. (200x160px automatically )

I just want that the image crop to best size, to show 2 images per row. With less empty space... using this blank or black space, to make image bigger.

My available space is width=214px for each image.