For digital images on PCs/Internet, dpi is not very relevant. The dimensions in pixels are. Having said that, the dpi may affect how fonts appear when you use Photoshop. In the old days, graphics apps may have worked with a default of 96dpi, many these days use 72. Those that work primarily for print may have their images set to 300dpi. When the image is shown on a web page, other factors come into play. If the HTML code forces the image to be 320x240, you lose the original resolution because it scales the pic down. However, in a quirk of vision, crappy images reduced in size may appear nicer even though there is less detail. Also, the size of the image may also depend on the screen size and zoom factor the user has set in their browser.
Thank you so much, Nanobyte! Wonderful information, and so simply explained, I think I've got the basics. I would like to sort of paraphrase a couple of points, however, just to make sure I'm on the right track, and I'd like to explain exactly what I'm looking for, as well.
First and foremost, photos make a HUGE difference on eBay. Here is a perfect illustration: Please compare this listing: http://www.ebay.com/itm/261099278887?ssPageName=STRK:MEBIDX:IT&_trksid=p3984.m1431.l2649
with this one: http://www.ebay.com/itm/110903085834
Both auctions sold/are selling the EXACT SAME TOP, but the first listing currently has a top bid of $13.49 -- that would be my bid -- the second listing sold for $79.99. That would be my auction. =)
Second point. eBay has been ramping up its efforts to entice buyers using smart phones and other mobile devices. "Last year alone, more than $5 billion was transacted via mobile on eBay, a figure we expect to double in 2012." Et cetera. I imagine it does wonders for impulse purchases.
eBay's new marketing campaign will target this demographic. A sneak peak at the new TV ads: http://pages.ebay.com/sellerinformation/sellingresources/holidaymarketing2012.html
I'm partial to "eBay Bad Dog", myself.
To facilitate eBay listings on mobile devices, eBay now offers 11 free photos at the top of the auction page. These pix need to be 1600 pixels on the longest side. They need to be high quality, because the app allows buyers to zoom in. Please see this active listing for an example: http://www.ebay.com/itm/120988199989?ssPageName=STRK:MESELX:IT&_trksid=p3984.m1555.l2649
However, some people don't like this app, and prefer to see photos in the listing itself. Scroll down in the auction above, and you well see my (extremely basic) HTML listing that includes all the same photos, but notice that the longest side is fixed at 600 pixels.
I've been a reporter for a number of years (and an unemployed reporter for even longer), and regardless of column width, every print publication I've ever worked for requires art to be submitted at 300 dpi. I associated this with high quality images and for years, I entered ebay photos at 300 dpi. They were enormous, took up loads of space and took forever to upload.
Using the information you kindly provided, I took one photo (recognize the top?) and resized them differently, according to eBay standards, and my own, at 72 dpi and 300 dpi.http://www.fozzybear.org/ebay/72dpi_1600.jpg
22.2 in x 17.4 inhttp://www.fozzybear.org/ebay/300dpi_1600.jpg
8.4 in x 6.5http://www.fozzybear.org/ebay/72dpi_600.jpg
2.0 in x 1.6 inhttp://www.fozzybear.org/ebay/300dpi_600.jpg
5.3 in x 4.2 in
If you take a PC screen, say 1280x960, a 640x480 pic will take up 1/4 of the screen area regardless of what the dpi is. Dpi is only important when printing. The resolution of a digital image on the screen is solely a function of the number of pixels. If you use IrfanView to change resolution ie the dpi, it has no effect whatsoever on the image. A 640x480 image at 320dpi is the same size as a 640x480 image at 72dpi. 640x480! If you print them however, the first will be 2" wide and the second 6.7" wide. You can only change the resolution for a PC/Internet image by resizing. Upsizing may be detrimental to quality since pixelation starts to appear. Doubling the pixel dimensions for example means that every pixel in the original becomes 4 pixels of the same colour in the edited version. This should not be confused with taking a digital photograph where the more pixels there are the higher the resolution.
This is the concept that flies so far over my head, I hear a sonic boom. The actual size of a photo is completely unimportant online, for some inexplicable reason, but regardless, I do get the fact that it just ~is~ this way, and I can memorize facts that I don't understand with the best of them.
Incidentally, those photos were all filtered with Noiseware Community Edition first.
Finally, my question is this: Will the naked eye, or eBay's Zoom app, result in a lower-quality photo if I use a lower dpi. I cannot see a difference, but I have a 15-inch diameter monitor.
From the first question you asked, it sounds like you are trying to save HDD space by reducing dpi. That makes no difference. What makes a difference is if you have original pics say 3000x2000 that appear on the web page at a size of 300x200. It's best to keep your originals at the existing res for future use. In the example I quoted, I would make a copy of the the pic 300x200 for use on the site and store the original elsewhere (dvd, external HDD etc).
I can put them on an external drive, but I don't really see why that's necessary. These aren't family photos, they're temporary photos that I hope never to have to use again.
THANK YOU SO MUCH NANOBYTE!!