You need two supply voltages for this board to work: motor supply, which goes directly to your motor (up to 35V for this L298N board, depends on what your motor needs), and logic supply of 5V, which powers the board's logic chips. If the motor supply voltage is between 7V and 12V, you can derive 5V logic supply from motor supply by enabling this board's ...
Try to use this code, without the library, and be shure to connect every pin to the correct arduino output! If everything is ok it should work! Check a tutorial here
int IN3 = 5;
int IN4 = 4;
int ENB = 3;
pinMode (ENB, OUTPUT);
pinMode (IN3, OUTPUT);
pinMode (IN4, OUTPUT);
digitalWrite (IN3, HIGH);
The Uno is a very limited platform, perhaps surprisingly, given its wide range of abilities and built-in hardware features. The two most glaring limitations for you application are its 16MHz clock speed (relative to modern desktop processors) and thus its bandwidth, and it's non-expandable 2KBytes of RAM.
Image processing would be right out the window, and ...
analogWrite() Notes and Warnings
The PWM outputs generated on pins 5 and 6 will have
higher-than-expected duty cycles. This is because of interactions with
the millis() and delay() functions, which share the same internal
timer used to generate those PWM outputs. This will be noticed mostly
on low duty-cycle settings (e.g. 0 - 10) and may result ...