To enable zooming on images in the postcard and photograph galleries you will need to enable the zoom feature on your iOS device. This can be found in Settings>Accessibility>Zoom.
Once turned on, you can zoom in on images by using a double tap with three fingers. To move the image around, drag with three fingers. Detailed instructions can be found on the Apple guide to using zoom, which are copied below. These instructions work for both ipads and iphones.
Turn Zoom on or off
Go to Settings > General > Accessibility, then turn Zoom on or off.
Zoom in or out
With Zoom turned on, double-tap the screen with three fingers.
Adjust the magnification
Double-tap with three fingers, then drag up or down. This gesture is similar to a double-tap, except you don’t lift your fingers after the second tap—instead, drag your fingers on the screen. You can also triple-tap with three fingers, then drag the Zoom Level slider in the zoom controls that appear. To limit the maximum magnification, go to Settings > General > Accessibility > Zoom, then drag the Maximum Zoom Level slider all the way to the left.
Pan to see more
Drag the screen with three fingers. Or hold your finger near the edge of the screen to pan to that side. Move your finger closer to the edge to pan more quickly. Or, if you have detached the Zoom Controller, drag it.
Switch between Full Screen Zoom and Window Zoom
Triple-tap with three fingers, then tap Window Zoom or Full Screen Zoom in the zoom controls that appear. To choose the mode that’s used when you turn on Zoom, go to Settings > General > Accessibility > Zoom > Zoom Region.
Resize the zoom window (Window Zoom)
Triple-tap with three fingers, tap Resize Lens, then drag any of the round handles that appear.
Move the zoom window (Window Zoom)
Drag the handle at the bottom of the zoom window.
Show the zoom controller
Go to Settings > General > Accessibility > Zoom, then turn on Show Controller, or triple-tap with three fingers, then choose Show Controller. Then you can double-tap the floating Zoom Controls button to zoom in or out, single-tap the button to display the zoom controls, or drag it to pan. To move the Zoom Controls button, touch and hold the button, then drag it to a new location. To adjust the transparency of the zoom controller, go to Settings > General > Accessibility > Zoom > Idle Visibility.