Thank for your help. Finally, i found that it come from my desktop (exactly screen resolution).
When i view the original image with my desktop, it look like a square. I have took a picture from my desktop here: http://i1312.photobucket.com/albums/t530/langhoangal/myQuestions/original_inDesktop_zpsbab06700.jpg
But when i open it by my laptop, i can see it like that (i think you see like that): http://i1312.photobucket.com/albums/t530/langhoangal/myQuestions/original_inLaptop_zpsbf19a22c.jpg -> same with what i can see in my phone.
So, the problem is my computer screen display wrong. :) I have tried to adjust resolution and it ok now, i can see exactly what display on phone.
Many thanks for all of you! Cheer!