Unless you’ve made vector art, there’s no real good way to make your art larger without losing a ton of the integrity of the image, no matter what program you use. While you can fudge things here and there in Photoshop, any significant size difference and it’s going to get fuzzy and lose clarity. The key to getting the larger items on Society6 (and in general, really!) is just to start with a large image in the first place.
Whether you’re scanning your art or rendering it digitally, it should be at a minimum of 300 dpi if you’re planning to have it printed, period. I’ve seen people go larger, but 300 is usually enough. Your scanner should have settings you can fuss with to do this. I don’t know much about photos (and don’t really recommend taking photos for anything other than stuff that can’t be scanned), but most cameras have a setting to adjust how large you want the final images to be. An image can always be made smaller, but bigger almost always results in blurring and distortion. An image at 300 dpi will be a larger file size, but it’s necessary.
Most of my images were 300dpi to start with, but in some cases, like my color meme Kira and Jeeves and Bertie, they hadn’t started out with intent to be something other than a doodle, so they were only 200 dpi. Luckily, Kira had a background that was easily expandable, so that’s something else you could do if you have work that would be difficult to blow up. Using a high resolution can also help if you’ve drawn an image that’s a bit on the small side, but you should try to draw at least the size of the thing you want to print on if you know that’s where you want the work to go.
(For Baby Bean Bag Garak, I had to literally retrace the original images to a 300dpi file, which is kind a worst case scenario.)
Some of Society6’s upload sizes are quite large, but you don’t have to fill every pixel with art. My t-shirt ones usually only end up occupying the top half-ish of the image and the rest of the file upload is transparent. I do usually have to upload several times though (especially for the phones!) since Society6 doesn’t provide templates and things are sometimes off.
I hope this helps a bit!
