Photomath, available for most any mobile device. Yes, using the camera you get the problem into your viewfinder, and the expression is either simplified or the equation is solved. You don't even have to key in the problem.
This would be a nice tool for students to use in order to check that they complete practice problems correctly.
At this time the app can simplify arithmetic expressions, interpret fractions, decimals, powers, and roots, and solve linear equations. It can't comprehend higher level math like Trigonometry or Calculus, yet. Hopefully in the future, as the app was released just a couple months ago.