Thank you for all the answer. I just noted that the LunaTic has the feature of removing the background from the image. However, its usability is a big concern. For anyone who are doing stuff with the images, LunaTic is good. And I have some tips that you should straight to the Edit and search for these commands in the pop-up card:
- Remove background: Transparent background
- Resize the picture: Scale
- Convert file: Image Info