1 - Try to resize your pictures to no bigger than 800x600 (Avatars 125x125)
2 - Upload the pictures to the host of your choice.
3 - Copy the URL of the picture(s) from the host site you uploaded to.
4 - On the post screen click the IMG button, a window will pop up.
5 - Paste the URL from the picture host into the window and click OK.
6 - You can post more pictures in the post by repeating the above for each picture
Note: You must allow pop ups on Cartaholics for the Window to pop up when you click the IMG button. If you don't want to allow pop ups here you'll have to manually add the IMG tags to your posts.