Hello klemon10,
Thank you for reaching out to Apple Support Communities, and we'll be happy to help in any way we can. We understand you're having issues with low quality images in iMessage. Have you tried restarting your iPhone? This simple step resolves a multitude of issues: Restart your iPhone - Apple Support
"How to restart your iPhone X, 11, 12, 13, or later
Press and hold either volume button and the side button until the power-off slider appears.
Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
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."
We hope this helps.
Cheers!