Yes, you have to reduce the size of your picture in pixel size. If you have Adobe Photoshop you can use the "save for web" feature which I find the best for doing this, myself. If you don't, then you need to use whatever program you use to "fix" your pictures and go to the Image Resize and resize the picture to bring it down to the limits of the forum.
A bit of trial and error should bring you to the point of putting your pictures on.
Good luck.