1. A system comprising: a shelf to hold one or more of a type of item; a camera positioned above the shelf and having a field-of-view that includes at least a portion of the shelf at an oblique angle with respect to a plane of the shelf; and a computing device comprising: a memory, storing computer-executable instructions; and a hardware processor to execute the computer-executable instructions to: determine the type of item associated with the shelf; access acquired image data obtained by the camera, wherein the acquired image data is representative of a two-dimensional array of pixels, each pixel having a value and each pixel being associated with a set of coordinates within the two-dimensional array of pixels; access item data indicative of a height of the type of item; access physical layout data indicative of: a position of the camera with respect to the shelf, and a direction the camera is pointing with respect to the shelf; select perspective transformation data based on the height of the type of item and the physical layout data, wherein the perspective transformation data associates a first set of two-dimensional coordinates in a camera plane to a second set of two-dimensional coordinates in a virtual camera plane, wherein the virtual camera plane is parallel to and above the plane of the shelf; generate rectified image data by using the perspective transformation data to map the values for the pixels at the first set of two-dimensional coordinates in the acquired image data to the second set of two-dimensional coordinates; determine one or more features present in the rectified image data, wherein a relative size of individual tops of the type of item are within a threshold size of one another; and determine item count data indicative of a quantity of the type of item present on the shelf using the one or more features determined to be present in the rectified image data.