Final answer:
To scale a bounding box proportionately, typically the Shift key is held while dragging a corner handle of the box in graphic design and image editing software.
Step-by-step explanation:
When a bounding box is selected, the keyboard shortcut to scale the box proportionately depends on the software being used. However, in many graphic design and image editing programs, such as Adobe Photoshop, holding the Shift key while dragging one of the corner handles of the bounding box is the common method to scale an object proportionally. Similarly, in other programs like Adobe Illustrator or software with similar functions, the Shift key is also used for proportional scaling. This action ensures that the height and width ratio of the object remains constant while scaling.
When a bounding box is selected in design software like Adobe Photoshop or Illustrator, the keyboard shortcut that scales the box proportionately is Shift + drag the corner handle. By holding down the Shift key while dragging one of the corner handles of the bounding box, the box will scale proportionally, maintaining the aspect ratio of the original object. This is useful when you want to resize an object without distorting its shape.