What if objects in different sizes for createsamples and traincascade?

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I I have images on which a object placed in different sizes. For esxample, on first image he is in size 9x20 px on the background(size of image: 440x200 px), on second image 15x24 and so on. How I should choose parameters Width and Height for program Createsamples.exe ? I create vec-file from previosly marked images(-info file.txt). And how in will be affects on cascade learning?