Trust me its cold!
by DDayComment by bohemka:
Hey Doug, great photo, but if I can help with resizing I'll try... Forget about the DPI. That really only comes into play with printing photos, and even then it's a long, tricky story.
The max file size limit is 300kb, but the tradeoff of sacrificing the "best" quality at that file size is well worth making sure the photo is as large as it can be. There's no noticeable difference in quality at that size, but smaller presentation is definitely noticeable. I made the same mistake when I was new and someone helped me out, so here's me trying ;-D
Best practice seems to be to reduce your photo by steps toward 800 pixels wide or tall. Basically, if your image is 4000-odd-pixels wide, reduce is to 3200, then in half to 1600, and in half again to 800. Do you sharpening at this last step. Many methods are available, but you'll see exactly what you're going to see online. When converting to jpg (or saving for upload) use the Save for Web option, and use the quality slider to get your file under 300kb. For me it's about 50/50 whether I'm at 100% or below, and when I'm below I cannot tell the difference.
I hope this helps, even a little. Don't be afraid to search in the forums for similar topics or others that you might be interested in. And even start a thread to get fresh opinions. Best of luck!