This is a really good attempt. I'll suggest that for now, your focus shoud just be on training your eyes to see "proportions" more correctly. Make lots of line drawings with a focus on proportional accuracy. Ignore complicated stuffs like shading for now or "contrast" like most people are suggesting as that will only confuse you more. As you get better, you can incorporate other fundamemtals. Have fun!

As others have said, increasing the contrast by adding deeper shadows would help, however I suspect there is something else that could help break away from the "cartoony" feel that you're seeing. Our brains are masters of creating patterns in and simplifying what what we see. This often comes into conflict when drawing because there is a disconnect in what the brain remembers about how features should be shaped verses what our eyes are actually seeing. For example: In the reference image you can't actually make out the majority of the eye. There is light hitting part of the upper and lower lids, but everything else is completely in shadow, including the white of the eye. There is the impulse to overcompensate and define the whole eye, even if we can't see it because the brain knows how eyes "should" look based off past experience. Another example is the placement on the collar. We have a tendency to put them too low because when "know" it rests on the base of the neck. In the photo, however, the collar has a lot of bulk and covers the majority of the back of the neck. Training yourself to recognize when your brain is filling in info based on your backlog patterns and symbols and instead drawing only what you see, is what what my college art professors called "using you artist eyes." I hope I explained that in a clear way. It was a concept that took me a while to grasp but helped me immensely when I do realistic portraiture.

so i think you need to work on your fundamentals overall. portraits are not easy at all, it requires knowledge in many aspects like anatomy, form, shading, values, edges, perspective, etc. the first thing is form. youre thinking of a 2d photo, but remember, a head is a 3d object that exists in 3d space. you can look up the asaro head or planes of the head, to see that you can divide the face into flat planes. each plane has a different angle. you can also feel this on your face, the nose bridge won't have the same angle compared to the back of your head for example. therefore, each plane will interact with light differently and have different values. thats why you need to think of form first if you want to have good shading. you can use any digital art software to color pick the photos, you can see that the values in the cheek bone ( near the eye ) is lighter than the cheek / jaw area. because the cheek bone is facing up, its catching more light from the sky so its brighter. ( both of those areas look very similar in values in your drawing, making the face feels flat ) the mustache is white, so it should be brighter than the skin tone and clothes. but in your drawing, you made it the same value as the face and clothes. the nostrils should be black, cuz there isnt a lot of light reaching them, they're holes. but the chin is as dark as the nostrils ( which is incorrect ), its catching more lights than the nostrils. there are a lot more things to talk about but i think it could easily be fixed after some studies. in short, try to think analytically, and understand what youre painting exactly. i would recommend studying basic shapes like spheres, cubes, cylinders, etc. or study each fundamentals on each own instead of tackling all of them at once. of course, its not a rule, but i think you its more efficient that way. do whatever makes you feel good. sorry for the rant lol, but i hope it opened up news way of doing art for you

While I do agree with the others that you need more contrast, I think what will make your drawing more realistic is to know the structure of the features. Because without the structure, you might just be blindly copying the values you see in the source image without understanding how the like interacts with it. Another thing, if you know the anatomy of the face, then you will be able to render the face to get it closer to the source image. For example in the area of the nose, you only indicated it through the use of an outline, when in reality, there are many different planes in the nose all with different values. And these things are the key in making your drawing seem more realistic rather than cartoonish. You effectively draw what you don't know. Keep working on it and you'll get the hang of it for sure!

I agree with the others about needing more contrast and softening the hard lines. If you do increase the contrast remember in the darker shadow areas the level of detail decreases, you can see an example of that in the eyes under the cap brim in your reference photo. Adding more detail to the areas in the light (moustache, hair, cheek bones, etc) will make a big difference too.

It needs more contrast to not have that cartoonish look. Also try to avoid harsh lines to divide areas of the face. Nice work!

I wouldn't call this cartoonish, but it is missing something to get to the level of realism it sounds you are trying to achieve. I'm not really familiar with realism, but I do know that most of the time adding an outline breaks the illusion of realism since they don't exist in nature. This means relying on shading and values to transition between features and forms. Stan is obviously a good person to study, but also check out Stephen Bauman. He is an instructor here, he did a 3 hr live demo/q&a for proko2 last week and has a youtube channel with a lot of tutorials https://youtu.be/EV9MuMfvPxA I hope this helps

I think you need to use loomis method for this making potrait of this photo