I have seen quite a few misleading requirements for image submission. Here’s an attempt to clarify some terms.
ppi and dpi both refer to the density of the image. How much information is contained in the file for the screen (ppi) or printer (dpi) to read.
The ‘size” (both file size and size in inches) of the image in inches can be all over the place by changing the density of the image using ppi
The problem is that an image we use to view on the internet usually wont have the amount of information (pixels) required for printing a smooth image. If we take the best image our camera can shoot it will be too large to see on the screen or take too long to download. Therefore we use different versions of our images for printing and viewing on the web. Generally 300ppi for printing (which converts to about 150 dpi in the printing process) and 72 or 96 ppi for viewing onscreen.
The above images are 600 pixels high and changing the ppi (Resolution or density) does not affect how they look on screen but you can see that the size in inches has changed radically. That is the size of your print. At 8.3 inches that flower will not look as dense and clear as it will at 2 inches. Thats why when you are asked for an image for printing they generally ask for 300 ppi. If when you change the setting to 300 ppi and the size is not large enough it’s time to look for a new version of that image. You could click resample Image and have the software try to fill in the gaps but you are doing your art a disservice. It’s best to maintain a folder of full resolution images in a non lossy format such as tiff or psd just not jpeg. From there you can always resample down to a smaller image for the web.
You can usually tell by file size if you are on the right track. for printing it’ll be 3 mb or more depending on how many inches it is at 300 ppi and for the web (72ppi) under a megabyte.
PPI-Pixels per inch
a screen measurement, usually 72 ppi for mac 96 for pc. No matter what setting you declare, 300 ppi or 72 ppi, the screen you are looking at has a certain amount of pixels to use and thats that. (see images below)
DPI- Dots per Inch
a printing measurement. The more dots the smoother the image will look. 300 dpi is good, Fine art books use 600dpi and newspapers 170dpi