my images won't resize in WordPress

I have been resizing images in the Visual HTML editor for my WordPress site for over a year and everything has worked fine. I just started a new WordPress site and now when I resize images in my document using the visual editor, the images show that I’ve changed them, but when I preview the page, the resized image doesn’t show up. The image stays the same. But that’s not how it looks in the editor. The editor shows the resized image but the preview does not. Any ideas?