Since we have introduced one-piece covers, we have seen a number of covers that have trouble printing. This is because our automated cover creation process created a PDF that was flattened to a single layer. Although, it is possible to create a very complex PDF using Adobe Illustrator with many layers, fonts etc. do not do this.
Also, you should avoid transparencies and transparent areas in your image files, as these cause unsightly light gray or white areas in the printed material.
The more complex the PDF, the greater chance that the process of rasterizing for print will generate errors. If you've created a cover PDF that uses fonts and separate images, your best option is to open the PDF in Photoshop — it will automatically ask for DPI (300 is optimal) and color palette (choose RGB). It will then rasterize the file to a single layer. Crop marks will need to be left off of the uploaded PDF.
Note: All printed books -- not just Lulu books -- can have a slightly offset spine. Some of the spine may spill onto the cover, or some of the cover onto the spine. The difference is minor and won't be greater than 1/8th of an inch. Still, because of this, we recommend you don't use sharply contrasting colors for your spine and covers.
