I tried adding custom entries in the exif dictionaries I received from an image. This didn't work. I'm assuming this is due to the fact exif is a standard that is already defined.
Basically I am trying to create a metadata tag that can be placed in jpegs that will have no character limit.
I read that XMP metadata tags do not have character limits. Is this true? If so how would I create these on the iPhone?
Thank you.
I'm not sure what you've all tried code wise, but Caffeinated Cocoa has a pretty good blog entry on Image Metadata that I've used in an application for a client a while ago that might help you.
Also, the SO post Problem setting exif data for an image looks like it references the Caffeinated Cocoa. Although this question is a little over a year old, it still might help.
Try giving these a shot.
来源：https://stackoverflow.com/questions/6567240/how-does-one-add-custom-metadata-tags-to-an-image-on-the-iphone