By just looking at an unlabeled picture, how do you know it is a protein?
Shapes
This is a common way of illustrating a protein and is often called a &quot;protein cartoon&quot;. There are other common ways of illustrating proteins.
This cartoon shows you where α helices are (spirals) and where β sheets are (arrows) which are important structural elements. The strings connecting those structural elements are flexible &quot;loop&quot; regions.
If you want to query this against other structures and see which protein it is, check out PhyreStorm. You'll need the PDB file, not just an image.
Colour
The colouring is also common. The N-terminus (the first amino acid) is coloured blue, and the colours go through the rainbow to red, the C-terminus (the last amino acid in the polypeptide chain).