Attachments have to be less than 1,000kb. It used to be that you could only attach 10 pictures with a total of 1,000kb per post, but IIRC, the number of pictures may have been changed...as long as they total under the 1,000kb.
It happens that I just took some pictures today, and they came out of my (Nikon) digital camera at roughly 4.4MB each. I have used IrfanView to rework them by cropping, resizing and compressing to post them. At this point, I'm not sure how big they are, but likely around 100 > 200kb. I'ma gonna post them in the "What did you do in the shop today" thread.

Steve
Edit: The largest of the 4 came out at 119kb and is 800 pixels wide. Much over that width and you may need to scroll back & forth to see the whole width, which nobody wants to do! Some have been posting pictures that never get over 330 pixels wide, which just isn't big enough to see anything. People use various ways to get their picture down to size, most of which don't yield a predictable result, IMO. I have tried to use Olympus and Canon software and couldn't figure out how to make it work. My brother suggested IrfanView, and in a few minutes had figured it out...all by myself. Therefore, IMO, it's superior to both Olympus and Canon software. The pictures I posted were taken with a Nikon, and I never even considered trying Nikon software! IrfanView is "Freeware", so the price is affordable...it's FREE! I got it off the TuCows download site. You have to download the one appropriate for your computer, so watch that. Others will be along shortly to tell you how they do it. Which is minimally useful and mostly confusing.