@cidelab, Instead of using a modal windows showing a larger (full screen) image, an alternative might be to adapt the layout of the page/image to cater for different screen sizes.
Based on the width and/or screen density of the device, such a responsive webdesign could then:
- Alter the space allocated to the image. E.g the image is displayed/zoomed at 20-25% on desktop and 100% on mobile.
- Display different images with different pixel sizes: Resolution switching.
This could save the mobile user costly and time consuming bandwidth.
- Display different image content (e.g cropped or portrait/landscape): Art direction.
I think a modal popup showing a large size image might be of value on a desktop because there is ample space to show the image 4-5x larger. That space is not available on mobile.