Former food products (FFPs) are alternative feed ingredients used in livestock diets. Although the processes of transforming FFPs into animal feed often include mechanical unpacking and grinding, the final products may still be prone to packaging contamination. Common materials of packaging remnants found in FFPs are aluminium, cellulose, and plastic. Therefore, it is important to investigate and to provide information regarding the size and shape attributes of these materials to improve processing techniques in the feed industry. A total of 441 packaging remnants from 17 sources of FFPs were included in this study. Fourier transform infra-red spectroscopy coupled with an optical microscope was used to identify the material of the packaging remnants, which resulted in a categorisation of remnants consisting of 44 aluminium, 308 cellulose, and 89 plastic remnants. The categorised remnants were observed with a stereomicroscope and were subsequently measured by a digital camera and image analysis software. Each measurement contains 21 size attributes and 9 shape attributes, some of which were derived from calculations. The distribution of values for both size and shape attributes overlapped between the three materials though aluminium remnants were on average smaller (p < .05) in size and more regular (p < .05) in shape compared to cellulose and plastic ones. Also, aluminium remnants showed a narrower range in most of the size and shape attributes. Through the information provided by the image analysis and the measurements, it was concluded that the obtained values in size and shape attributes had broadly spread distributions that overlapped for different materials.