Dpi, or dots per inch, refers to the number of dots printed in a linear inch. The pixel dimensions of your digital image and the size it is printed at, will determine its resolution. Pixel dimensions also determine file size.
If you are planning to scan some images for use in your print project, make sure the scan resolution at least 300-350dpi, at the final output size.
If you were to scan a stamp at 300dpi you could then print it at the same output size and it will print clearly. However if you enlarge the stamp in Photoshop to make it 10 times the size, the image will appear horribly pixelated…why?
Because now the stamp scan has just 1/10th of its original resolution! Photoshop will simply do its best to enlarge the image dimensions using interpolation – basically adding in new pixels. To counter this, you must scan your image at 3000dpi! Enlarging it 10 times the size will then result in a 300dpi image when printed.