Error on resize image

Can someone help me to solve this problem. When I done make a doodle on my canvas, then I press the ok button and continue to edit again with resize image, but it show that image should have to be in jpg format. What should I do ?

Taifun resize block will only handle jpg. Save your canvas image as a jpg.

How can I save the canvas image as a jpg?

Use the '.jpg' extension.