[Mee-n-Mac]

I've read the FAQ and searched the forums but I didn't find any rules/restrictions/recommendations (beyond the basics) on posting photos. I would ask the following questions ;

1) What type of files are allowed ?
I assume 'normal' JPEGs only.

2) What size files are allowed ?
I didn't see any restrictions and there seem to be 2 sizes listed for each photo. I assume 1 or both are generated automagically when the pic is uploaded ?

3) Are there guidelines for picture dimensions and/or compression ratios ?
Of course this is related to #2 above, but is it desireable (even if not strictly required) to make, via cropping and/or resizing, the long side of the pic no more than a certain pixel size (ie - 800 or 1024 pixels) and then compress to get under the max size above ?

If I've missed the above info someplace, then I thank you in advance for directing me to it. If there aren't hard rules for the above then what do the pic posting regulars use as guidelines ? What does the Webmaster recommend ??