Pixels come from inches times DPI
A trading card is 2.5 inches wide and 3.5 inches tall. Multiply by the print resolution to get pixels: at 300 DPI that is 750 x 1050; at 450 DPI, 1125 x 1575; at 600 DPI, 1500 x 2100. Whatever the resolution, the ratio is 5:7.
The bleed box
Cards are printed slightly larger than the finished size and then trimmed. Snapshot's print area adds 1/16 inch on every side, making a 2.625" x 3.625" bleed box. At its print resolution of 450 DPI, that is a 1181 x 1631 pixel raster.
You do not need to produce that file; the builder renders it. It matters only as the reason to keep important content away from the edges of anything you upload.
What to upload
For a finished design of your own, supply a 5:7 image at 1500 x 2100 pixels for the best result, and no smaller than 750 x 1050. An image at another ratio is stretched to fit the card rather than cropped, so crop to 5:7 first. JPG, PNG, HEIC, and WebP are accepted.
For a photo going into a template, there is no fixed pixel requirement because the builder crops and scales it, but at least 1000 pixels on the short side leaves room to crop without softness.
The MEGA Card
A MEGA Card is 11" x 15.4" in the same 5:7 proportions. Its design is rendered from the same card you built rather than from a separate file, so nothing changes about what you upload.
