Question

What is the difference between congruent and similar images

Answer 1

Congruence and similarity may be thought the same, but they are actually very different. If an image is congruent with another, then they are exactly the same, with not a single thing that is different between them. They are identical. If two images are similar, then they aren't congruent. There may be some differences between the two, but not big enough change the way you view the image. 

Answer 2

In a congruent triangle, sides and/or angles have to be the same

In a similar triangle, they have to be proportional

hope this helps