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Actually, it's even better to rotate the cover slightly (like 7-10 degrees) before scanning it. This reduces the possibility of a moiré pattern as much as possible. It's better than any "anti-moiré-filters", because they are usually nothing but a (gaussian) blur filter in order to get rid of the moiré patterns, blurring the outcome massively.

This procedure, in combination with a high-resolution scan (600 dpi or whatever native resolution the scanner has, without interpolation), gives quite some decent results - even with low-end scanners. Scaling it down to the final size should preferably happen in 2-3 steps as one can add some slight (!) sharpen filters with every step, preserving way more details (without over-sharpening the image) than with a one-step downsizing.

Yes, it's slightly more work to do, but the results are decent, even with low budget scanners and without PhotoShop.