I couldn't find this documented anywhere, but after much experimentation here are what I believe the correct dimensions of the images to be. Note that if you only include the @2x retina image, it will be automatically downscaled for regular displays.
icon
- 29x29
- 58x58 (@2x)
- Appears in the mail app, and in notifications about the pass, but not on the pass itself
- This image is mandatory, the package will not open without it
logo
- 30x30 to 300x30
- 60x60 to 600x60 (@2x)
strip
- StoreCard - 310 x 123 or 620 x 246 (@2x)
- EventTicket - 310 x 84 or 620 x 168 (@2x)
- Will be center-cropped if it is too high
thumbnail
- up to 80x90
- up to 160x180 (@2x)
- will be downscaled if too big, will not be upscaled if smaller than the max dimensions. So an 80x80 icon will appear as 80x80.
background
- 312x398
- 624x796 (@2x)
- This appears blurred behind the pass.
- I'm not 100% sure about these dimensions, its hard to tell because of the blurring, but they seem to work.
footer
Not sure about this one yet, 200x30 seems to work well.