Right click of a mouse displayes a menu which will be displayed near the cursor. You can choose from two functions
Save page as image
Save selected area as image
The latter one can be used only when a selection is already present.
Both functions store portion of viewed page to an image file. Format of the image file is depending on the system and version of Qt.
Save page as image stores actual viewed page to an image file. If only a part of a page is displayed, only the part of page is stored.
Save selected area as image stores only selected area. If selected area is fragmented or has not a rectangle shape, then a bounding rectangle of selected area is sotred. If selected area is bigger then actual displayed part of page, storing area is cropped with same rectangle as page is cropped in Save page as image.