just an fyi according to my understanding of things:
PPI (pixels per inch) and DPI (dots per inch) are not the same thing although many use them interchangeably.
ppi and dpi are both used only for determining hard copy (print) image sizes and are not used at all for sizing images for screen display. For a given screen the only thing that determines the size of an image on the screen is the overall width and height in pixels of the image.
DPI is solely a printer property and represents the number of ink dots it will lay per inch of paper in the X and Y directions. 1 DPI does not equal 1 PPI.
A general rule of thumb is you should have 300ppi minimum to make a good quality print copy which means if you want an 8" x 10" print, the original image size (and not an enlargement of an original) needs to be at least 2400px x 3000px.