Welcome to the Apple Support Communities!
I understand you are not seeing photos in text messages on your Apple Watch. Are you able to see the photo in the Messages app on your iPhone? If your carrier settings for your iPhone include MMS messages and your paired iPhone is powered on and connected to Wi-Fi or cellular, then you should be seeing photos on your Apple Watch.
Take a look at the resources below for more information:
Read and reply to messages with your Apple Watch
How to use your Apple Watch without your iPhone nearby
To receive SMS, MMS, or push notifications from third-party apps on your Apple Watch Series 3 (GPS + Cellular), your paired iPhone must be powered on and connected to Wi-Fi or cellular, but it doesn't need to be nearby.
To use SMS/MMS on an iPhone, you need a text-messaging plan. Contact your wireless carrier for more information. You can also set up your other Apple devices to send and receive messages from any Apple device.
If Wi-Fi is unavailable, iMessages will be sent over cellular data. Cellular data rates might apply.
Enjoy the rest of your day!