1. I heard singing. (OK; singing functions as an object.)Originally Posted by RL
2. I heard her sing. (OK; sing functions as an object.)
I (subject); heard (verb, past tense), her sing (verb's object). Note, 'her' is a pronoun. It takes 'sing' as its object. Objects do not carry tense.
3. You looked a lot like her. (Used to look; at that time, in the past, when the photo was taken, you looked like her)
4. You look a lot like her. (At the present time, now)
Thank you so much, Ms. Cas! You've been very helpful. :)