I am wondering how can I achieve this pencil effect on an image using Photoshop or other software.
Is it some kind of painting? Or is there some converter tools? What I want is to convert a simple image to this effect.
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There are plenty of edge finding and cartoonizing filters for Photoshop, GIMP, Paint.NET etc... as add-ons and also included. Applying them to a photo can create black lines and reduce the number of colors.
Mostly (see NOTE1) the result is too good to be done by filtering only. Theoretically they could have been edited manually starting from a filtered photo (or a composition of several photos) I do not believe it. I bet at least all human characters are totally redrawn manually.
Cartoonizing filters cannot decide which are the major outlines that a human draftsman would draw at first, if it must be line art. The next image shows what cartoonizing makes typically:
All strong contrast borders are blackened with no idea which of them should be long and solid to create the border of an object. It's possible only for a human draftsman. Of course, the user could help the filter by preparing the image to have high contrast at the right places or by clipping the objects apart.
In your examples the white stroke around many shapes is a trivial layer effect or vector stroke after the shapes are constructed (not trivial) as separate vector objects or layers.
The person who drew them has so steady hand and eye that he/she could as well make high quality drawings without leaning against a photo. See that woman who has just got some papers. No filter can make her from a photo.
If a beginner wants as good results and succeeds to get them, then after fighting trough the job he can very truthfully say "I'm no more a beginner".
NOTE1: One can easily spot some black lines that aren't placed carefully. They are in the clothes.
Bends, bumps and foldings in the clothes are difficult. See an example:
In the left there's a photo with an outline and 3 more visible edges. The outline around the cloth is stroke effect. The three other nearly vertical lines are drawn manually. The same without a photo shows that there's no contradiction with the photo.
We can see there's some well visible bends. Can I add some nearly vertical black curves to underline them like the edges? The answer is NO, they would not fit. . In the photo the bends are gradients. The watcher would see there's something sharp.
Shading can be underlined with fine hatch. One must draw a bunch of curves which follow the surface curvature andinsert more lines at the dark areas or alternatively use there wider stroke. Engravers have done this hundreds of years.
Third and fourth images are a coarse demo of those "geodetic lines" and inserting darkness with more lines. Inkscape's "Interpolate Subpath" has been used to copy the curves.
A sharp border between two differently colored surface facets can have a black line, if there's the photo under them as a glue "this is not a hole, but a border"
If you like to practice drawing the lines, a good test is to close the photo layer temporarily. If it still looks out right, you can be sure the lines fit well. But as mentioned, lines on sharp color borders can be fine with the photo altough they easily look out totally unrelated without the photo.