1. An image processing device comprising: a processor; and a memory storing computer readable instructions therein, the computer-readable instructions, when executed by the processor, causing the image processing device to perform: preparing image data representing an image, the image including a target region consisting of a plurality of target pixels, each of the plurality of target pixels having a pixel value; classifying each of the plurality of target pixels as one of an object pixel and a background pixel other than the object pixel, the object pixel constituting an object represented in the target region; determining whether or not the target region satisfies a first condition related to a relationship between the object pixel and the background pixel to make a first determination result; judging whether or not the target region is a letter region representing at least one letter based on the first determination result; identifying a region of the image as one of the target region and a peripheral region surrounding the target region based on the image data, the peripheral region consisting of a plurality of peripheral pixels each having a pixel value; classifying each of the plurality of target pixels as one of the object pixel and the background pixel based on the pixel values of the plurality of peripheral pixels; classifying a target pixel of the plurality of target pixels as the background pixel when a difference between a pixel value of the target pixel and an average value of the pixel values of the plurality of peripheral pixels is smaller than a second prescribed value; and classifying the target pixel of the plurality of target pixels as the object pixel when the difference is greater than or equal to the second prescribed value.