Hello, Sean! Does this happen with every photo someone sends in iMessage? They may need to resend the photo, as it may have gotten corrupted during transmission.
If it happens with every photo, first try closing Messages and reopening it. See if that solves the issue. Follow these steps:
- Swipe up slowly from the bottom of the screen.
- Pause for a moment until all the open apps show.
- Scroll through the different apps until you find Messages.
- Swipe up on Messages to close it.
You may also find it beneficial to restart your iPhone:
1. Press and hold either volume button and the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.
(Restart your iPhone - Apple Support)
I hope this helps!