To process uploaded file for certain content type, how to? For example:


A new content type Photo is created
The optional core module Upload is enabled
Such that users can upload JPEG files


How can I:


In view mode of a Photo node, show a small "View EXIF" button next to the Photo  
When the user click the "View EXIF" button, my module show some EXIF info about that photo


i.e.:


add a button only for a particular content type (Photo in this example)
trigger a hook to process a uploaded file (a JPEG file in this example)


Thanks!
Use the Exif module to grab your exif data from the uploaded image:

Use some simple theming (eg: create node-photo.tpl.php if you are using d6 and content type is called 'photo') - there do some simple jquery show / hide type stuff with a div wrapped around your exif data.