We recommend using label printers with 300dpi (for sharp pictures) thermal transfer and direct thermal label printers with built in LAN ports and reliable drivers from Seagull Scientific.
People sometimes use Zebra label printers, which are also OK. Label printers should have a 300dpi head, a LAN port and Seagull Scientific printer drivers.
People sometimes use DYMO LabelWriter printers. These are direct thermal printers for which you can only use DYMO stationery which comes in fixed sizes. They lack a LAN port so you need to add a printer server. They are inexpensive, but suitable only for producing moderate numbers of simple labels on plain, not too large stationery.