I agree with using PNG, I find they have smaller file sizes than JPEG as well (and there isn’t the serious quality issue which JPEG suffers. 
PS: aPNG is currently supported in Firefox and Opera with Safari and IE left out in the dry. Though I doubt it’ll get much swing as I’m more in favour (along with most other people) at getting animated SVG past the gates (which is even better due to it being vector not raster).
I had to look up the reference (I don’t know disc-world) but pretty funny 
I must say that I’ve never been able to get a smaller file size for a PNG than a JPG for a photograph. Graphics, yes, but not photographs.
Christian it is sometimes possible to get smaller PNG-8 than JPEG if the photograph is greyscale and not too complex I’ve just done it with a picture of a person… Though it depends on the image and how you save; I used an “uncompressed” 201 KB TIF and exported separately as; 100% quality JPG (77.5 KB); and as PNG-8 (70.9 KB). Perhaps I should have been more specific with the JPG settings then it might have been smaller but the PNG won in that instance (note: JPG was at 100% quality).
True, but as mentioned above, nobody use 100 percent JPG compression online (and there’s really no discernable difference for most photographs). While there may be exceptions, JPG will almost always compress photographs better than PNG, is a quality loss is acceptable.
While I will not blindly use jpg’s for photograph-style images, when I’m in doubt I do as Felgall suggests and save in various forms to see who’s the smallest.
JPG usually wins. It looks okay and is way smaller. Again, this is for a photographic image.
If it’s photographic but small, I may just go ahead and let it look a bit funky and use an indexed file. http://michigan.gov/images/demo/banner4_279379_7.gif She looks indexed, but if you had some good reason to mix a logo (best as a png) with a photo that size, would you bother saving as jpg (or unindexed png?). I wouldn’t.
Why is it a gif? The word has apparently not gotten out about PNGs. I see gifs al over the place where pngs would be a bazillion times more awesome and often smaller size for exactly the same quality.
I personally recommend .GIF as it is lighter and it loads fast.
I think one problem with pngs taking so long to become more widespread is because of IE not supportting certain kinds of png images. That is, many have heard of needing a “png fix” not realizing that certain pngs don’t need it. That and I guess old habits die slow.
Yes, I agree generally typically nobody would use 100% for web. I fully understand what you mean the fractal JPG compression with Lossy should win 99.999% on a typical colour photograph.
What I was trying to illustrate was a simple near “like-for-like” comparison even when the JPG was converted to true ‘grayscale’ (about 3 bytes smaller than I posted before) it was still larger than the PNG-8. When at about 80% it was around 14 KB. So yes, Horses for Courses.
Really, I just felt like allowing the PNG-8 to fairly and squarely beat the JPG for the photo. 
No problem - I like PNG too, and it’s certainly the best loss-less format that I know of. Was simply trying to prove my point
