What is the square scan code looking thing that appears on only some of my important and personal photos?

Tap on it what do you see.

Actually, it is for selecting and copying the text on the photos for pasting it elsewhere when needed.

1. detected text, tap .
2. Swipe or use grab points to select text, then do any of the following:

• • Copy Text: Copy text to paste into another app such as Notes or Messages.
  • Select All: Select all the text within the frame.
  • Look Up: Search text on the web.
  • Translate: Translate text.
  • Share: Share text using AirDrop, Messages, Mail, or other available options.

1. To go to a website, make a call, or start an email, tap the website, phone number, or email address on the screen.
2. Tap  to return to Camera.