How can I find brick part number from a picture?
You'll need to start learning the nomenclature for those pieces.
For example the long straight pieces you have there with holes on top are &quot;Technic, Brick 1 x 12 with Holes&quot;
The pieces with rounded ends are lift arms. You can browse through the list of them here or take a stab at their descriptions using the width and number of pin holes. For example the purple on you have there is

1 hole wide

9 holes long

as think as a normal LEGO brick (some are half that thickness)

Bent with 6 on one line and 4 on the other
so &quot;Technic, Liftarm 1 x 9 Bent (6 - 4) Thick&quot;