This enumeration determines the edge of the "paper" with which the image's "top" is aligned.
Values:
| IG_TW_OR_LANDSCAPE | Equals IG_TW_OR_ROT270. |
| IG_TW_OR_PORTRAIT | Equals IG_TW_OR_ROT0. |
| IG_TW_OR_ROT0 | Normal orientation. |
| IG_TW_OR_ROT180 | Rotated 180 degrees clockwise. |
| IG_TW_OR_ROT270 | Rotated 270 degrees clockwise. |
| IG_TW_OR_ROT90 | Rotated 90 degrees clockwise. |