1. "Drawing" cut in.
Copy and paste the picture into the Drawing. Use the selection toolbox in the drawing to select the desired copy of the content. In "Drawing"-New-Paste, save the pasted contents-save to the desktop (easy to find). The saving format is preferably jpg format.
2. Use ACDSee 5.0 software.
Right-click "Picture of Primary Mathematics Electronic Textbook"-select ACDSee 5.0 as the opening mode. Click the editor that comes with it, and check the box to delete the unwanted content. Click File-Save.
There are also many picture editing software that can cut pictures. These two softwares are the most commonly used and easy to operate.