A woman pointed to a picture of a dog in her mobile phone and said that I looked alike, not insulting, but I didn't understand the metaphor. We have a good relationship. Ask for an explanation.

I can't explain anything. First of all, this is just a joke, and it shows that you have a good relationship and are trustworthy people. At the very least, she trusts to joke with you and is not angry, but that doesn't mean anything else, that she likes you, and that she insults you. Girls like dogs, so it's normal to make a joke once in a while. But it seems that you like that girl.