They have very different aromas. But you asked how to check just by appearance. I did a quick image search on both. I used to regularly clean and check for insects both of these herbs by the boxful, so I was a little surprised to find all images of such green healthy looking cilantro.

Image credit: Growing Fresh Cilantro in your Garden or Small Farm

This must still be growing on the plant. Most of the cilantro we would get was from Mexico. By the time we get it in Chicago, it had usually become a little yellowed. Still healthy looking, but it is no longer a uniform color, being a mixture of light green and yellow.

Italian flat parsley on the other hand is usually a much darker green, and stays a uniform color until it starts to brown.

Image credit: Dark Green Italian (Plain Leaf) Parsley, 2 g

This image is of much healthier parsley than what you typically find in the grocery. But, it is a noticeable shade darker than the cilantro.

Also, if you look more closely at the shape of the leaves, the parsley and the cilantro both have a similar shape. But, the cilantro is rounded at the points while the parsley leaves comes to sharp points. È una differenza sottile, ma è un chiaro indizio.

Inoltre, anche se non è visibile, il coriandolo è molto più facile da spezzare con le mani. Questo non è così evidente se si rompe solo una piccola quantità. Ma, quando si rompono i mazzi, il prezzemolo è notevolmente più difficile e robusto del cilantro.