The 100kb limit may be a function of the forum software; I don't know if the images are part of the database, and if they are, >100kb apiece they could slow things down pretty quickly when you consider the thousands of images uploaded.
1) Link images in using IMG tags from a remote site like Photobucket or the ilk. The forum software automagically resizes them to a percentage of your browser screen if they're too big.
2) Get 50 quality posts - and you naturally seem to be posting quality - and you're eligible for an Album here with much more generous size limits. You link from it with IMG tags as well. This availability may be the other reason for the 100kb "anyone" upload limit; we want people to stick around, and there are direct benefits like image storage for those who do.
I size to a standard 800px for most of my image postings; it's not difficult to get those to around 200kb or a little more.
The best thing about a bicycle is that it uses no gasoline, therefore the chance of fiery death is greatly reduced.
First Catman, then Gary Burke and now Bigg Fredd - there's one heck of a coin club in Heaven.