A method for distinguishing between items of similar appearance that vary in size comprising: receiving, by an image processor, an image including a plurality of items; identifying, by the image processor, each item in the image; generating, by the image processor, a region of interest for each identified item in the image; determining, by the image processor, a dimension of the region of interest for each identified item in the image, wherein the dimension of the region of interest is expressed in pixels, characterized in that the method further comprises: determining, by a pixel-to-physical dimension ratio engine, a plurality of pixel-to-physical dimension ratios for each identified item using the dimension of the region of interest and a plurality of possible physical dimensions associated with each identified item; identifying, by the pixel-to-physical dimension ratio engine, a selected pixel-to-physical dimension ratio among the plurality of pixel-to-physical dimension ratios; and determining, by a size engine, a stock keeping unit identifier of each identified item in the image based on the selected pixel-to-physical dimension ratio and the dimension of the region of interest for each identified item, wherein the step of identifying the selected pixel-to-physical dimension ratio comprises: counting, by the pixel-to-physical dimension ratio engine, a vote for each pixel-to-physical dimension ratio of the plurality of pixel-to-physical dimension ratios; and identifying, by the pixel-to-physical dimension ratio engine, a pixel-to-physical dimension ratio among the plurality of pixel-to-physical dimension ratios that accumulated a maximum number of votes as the selected pixel-to-physical dimension ratio. receiving, by an image processor, an image including a plurality of items; identifying, by the image processor, each item in the image; generating, by the image processor, a region of interest for each identified item in the image; determining, by the image processor, a dimension of the region of interest for each identified item in the image, wherein the dimension of the region of interest is expressed in pixels, characterized in that the method further comprises: determining, by a pixel-to-physical dimension ratio engine, a plurality of pixel-to-physical dimension ratios for each identified item using the dimension of the region of interest and a plurality of possible physical dimensions associated with each identified item; identifying, by the pixel-to-physical dimension ratio engine, a selected pixel-to-physical dimension ratio among the plurality of pixel-to-physical dimension ratios; and determining, by a size engine, a stock keeping unit identifier of each identified item in the image based on the selected pixel-to-physical dimension ratio and the dimension of the region of interest for each identified item, determining, by a pixel-to-physical dimension ratio engine, a plurality of pixel-to-physical dimension ratios for each identified item using the dimension of the region of interest and a plurality of possible physical dimensions associated with each identified item; identifying, by the pixel-to-physical dimension ratio engine, a selected pixel-to-physical dimension ratio among the plurality of pixel-to-physical dimension ratios; and determining, by a size engine, a stock keeping unit identifier of each identified item in the image based on the selected pixel-to-physical dimension ratio and the dimension of the region of interest for each identified item, wherein the step of identifying the selected pixel-to-physical dimension ratio comprises: counting, by the pixel-to-physical dimension ratio engine, a vote for each pixel-to-physical dimension ratio of the plurality of pixel-to-physical dimension ratios; and identifying, by the pixel-to-physical dimension ratio engine, a pixel-to-physical dimension ratio among the plurality of pixel-to-physical dimension ratios that accumulated a maximum number of votes as the selected pixel-to-physical dimension ratio. counting, by the pixel-to-physical dimension ratio engine, a vote for each pixel-to-physical dimension ratio of the plurality of pixel-to-physical dimension ratios; and identifying, by the pixel-to-physical dimension ratio engine, a pixel-to-physical dimension ratio among the plurality of pixel-to-physical dimension ratios that accumulated a maximum number of votes as the selected pixel-to-physical dimension ratio.