Upside down, boy you turn m

event_note September 27, 2013

Be aware that the BioID Web Service (BWS) does not auto-rotate images if the EXIF tag information is missing or wrong!

The EXIF (Exchangeable Image File Format) data of an image may contain the orientation of the camera while the image was taken. This is often the case if the device has an orientation sensor built in which is common in smart phones or tablets or digital cameras. Image viewing software and apps use this tag to rotate the image so that the top of the image is shown at the top of the display regardless of the orientation the camera had while taking the picture.

Let's illustrate that with the way an Apple iPhone saves images taken with the back camera. 

If you hold the iPhone in upright position with the button at the bottom the image you take would be rotated 90 degrees counter clockwise.

Phone in upright position

If you take a picture holding the phone at right angle (with the button on the right side) the resulting image has the same orientation as the scenery you shoot.

phone at right angle (with the button on the right side)

If you take a picture in landscape orientation of the display and the button shows to the left the resulting image would be upside down.

landscape orientation

And with the button pointing to the top holding the device upside down the resulting image would be rotated 90 degrees clockwise.

device upside down

If you display the image on the device or on a computer with image viewing software it is often auto-rotated in upright position according to the information in the EXIF tag 274. The BioID Web Service (BWS) also respects the orientation information in the EXIF tag. But if this information is missing, e.g. the EXIF tag info was removed by some image manipulation software or the orientation data is stored in some other format the BWS will not try to detect and rotate the image in upright position.

It is the task of the developer of the software using the BioID Web Service to ensure that the image is rotated in the right position!