I'm iso ways to avoid quality loss when uploading. Or, to at least up the quality a lil more using techniques in photoshop. I only know of two ways. One is Sharpen and the other is Apply Image > Soft Light. I currently made a sig and the quality is just really bad after uploading (compared to what is on my computer):
file> save as> .png losless! (or file>save as>.jpg> quality setting up to max) However with the .jpg the more it is downloaded and uploaded the more quality loss there is.
PNGs are not lossless uuhhhhmmmm... the only way to best optimize graphics for web use is pre-compression. Whereever you host your images (unless you do it yourself) check their max upload size and make sure you're image falls under that by save for web> jpg> and about 70-80 should knock it down. I can go into more depth with some other settings if it's still degrading. A lot of these image hosts use a serverside image compressor that will destroy your beautiful graphics. If your image falls under their max file size, it's wont get recompressed. PNGs are great if you host you own images, but in most cases, the file size is bigger than JPG, so while you save on loss, you get double compression which in the end is more lossy than a jpg. hope this helps! - clash
72 is optimal, and resolution would only impact printing. Higher res won't display any better in-browser.