The safest option is a PNG with transparent background, at actual print size, 300 dpi, in RGB or the profile the printer requires. For simple logos a vector file can also be sent, as PDF, SVG or AI, with fonts converted to outlines.
Avoid images taken from social media or artificially enlarged: edges come out blurry. Avoid lines thinner than 0.5–1 mm and very small text, because they do not transfer cleanly. Check that the artwork has no semi-transparent edge, which turns into a white halo with DTF.
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