You can post fairly large pictures which are under 100k using the save for web function in Photoshop as described here:
Size, Quality and/or Format your Attached Images.. (Click here
This may also help some...
How to attach Files/Images to your Posts or Threads?(Click here
If you want to post a larger resolution that is over 100K then you can host your image on your own site or elsewhere and attach a link, but also please attach an under 100K version here (so the thread remains useful in the future, regardless of external links).
Alternative Image Hosts if you do not have your own site are: ImageVenue.com (3Meg max, free) or pixentral.com (2Meg max, free) or photobucket.com (1 Meg max free,... 5 Meg PRO) or mediafire.com (100 Meg per file) ... then post a link here in the thread to the site that is hosting your larger image.