Corners barely graze inner-edges of the frame's borders

Note that for the initial rotation angle shown in Figure 1,

• the corners of the image
• almost touch the inner-edges of the borders on the frame.

If you run the program and rotate the image,

• you will see that the size of the frame is such
• that the corners of the image barely graze the inner-edges
• for those cases where the diagonals of the image are horizontal and vertical.