answer:I believe that it depends on the DPI (dots per inch) of the printer (you will need to find this out). If, for example, your printer was 300 × 300 DPI, then for every inch (every 2.54 cm) it can print 300 pixels. So, the picture is 600 × 300 pixels as you say (which is actually quite small), and you were to print it on a 300 × 300 DPI printer, to have the most accurate and best quality printout at 1:1 ratio, the physical image will only be (600 ÷ 300) × (300 ÷ 300) = 2 × 1 inches (approx. 5 × 2.5 cm). The higher the DPI of the printer the larger the image can be (for example a 600 × 600 DPI printer could print that same image double that size and it would look just as good). This means if you want to make it poster size you will have to use a program like Photoshop to scale it much more larger – you will probably need to experiment a bit because there is no way of finding out how large an image can be scaled before it is of unacceptable quality except by judging it yourself. If you are using the 300 × 300 DPI printer and want to print an A3 sized (297 × 420 mm, or approx. 11.693 × 16.537 inches) version of the 600 × 300 pixel photo, [this is where it gets hard because printers are measured in inches whereas standard paper sizes are measured in millimetres] you will need to resize the image to about [we can’t get it exact because of the difference in measuring systems, but it’s close enough] 3508 × 4961 pixels, whether or not this looks good is for you to judge, but I would guess it would look very blurry. Sorry if this sounds complicated (all those numbers!), if you still need clarification feel free to contact me.