I haven't made any prints from my images, yet, but I have been researching it for some time, now, and I'm rather confused about a couple of things.
First, I have encountered a lot of websites that do print-on-demand framed prints in various sizes, yet nearly all of them use JPEGs to do these from. My understanding has been that JPEG is a lossy compressed format that is only useful for posting images on a website and that the standard for printing has always been TIFF. So, how are these companies able to produce anything worth framing from a JPEG?
Second, I have seen several services online that offer large format poster-sized prints and some of the resolutions they claim to accept for this seem awfully low for this. Also, some of them claim to be able to do it, again, from JPEGs, rather than TIFFs. What's up with that?!