I just load my digital camera pictures on my Hard-Drive, in 'Pictures' or 'Documents'. I prefer JPEG images and reduce them to 300KB or smaller.
Detailed - sharply focused 'area' pictures, (front-sight/ muzzle-crown, left-side of receiver markings, side and top images of rear-sight, and stock markings), are more useful than complete rifle photo attempts.
I still have 'Microsoft Office 2010' on my Desk Top computer and that allows all kinds of photo editing and cropping.
IMHO - Big pictures are a pain to look at and photos linked to other sites, eventually expire and the thread become meaningless in the future.
When you make a reply on the KCA Forum, there is a 'Browse' button (below) that lets you go to, find, and attach stored images (by selecting image and hitting 'OPEN' button).
Over to the left of the screen, there is an 'Attachments & Down Arrow', this creates more 'Browse Boxes' and can be used (repeatedly) to attach up to five photos to each post.
I hope this helps ... and keep your feet out of your pictures.
(attached: 298KB and 34.2KB - JPEG examples)