Uploaded images are the primary visual representation of the manufacturer's products. Manufacturers will often have multiple images of a particular product so it is important to choose the image the company most likely would want associated with the product and that best represents the product to the specifier.
The perfect image
Once you have selected your source image(s), crop these images to a square proportion (height matches width). Ensure that the image is clearly visible, appropriately centered and has sufficient background space or whitespace around it. The fixture in the image should not touch or cut off unless it is unavoidable; the result should be aesthetically pleasing. Being careful not to sacrifice aesthetics, always try to use as much of the source image as possible to maximize the image quality. Aim for consistent cropping choices across the manufacturer's entire line.
More than one suitable image
Choose the image that will offer the most consistency across the entire manufacturer's product line. For example, a manufacturer has a single product with an excellent high resolution image and a white background. This same product, along with all other products in the series have images at a lower (but acceptable) resolution with a blue background. The blue background images would likely be a better choice for all the products.
If you find a product with several options (like different sizes) with several versions pictured, choose the best standard image.