I'm not a good one to answer this as I struggle with it myself. I think I have read here that the are some free software sources and/or use a site (like Photobucket). The file/picture needs to be under 500KB - which is kind of tough with modern cameras. I use a Kodak "Easy Share" camera and software @ 8.2 megapixels and the files are usually around 1.75 - 1.90MB. I end up cropping and saving (repeatedly) to get the file down to size. However, what I end up posting is about 1/4 of the original picture.
Once you get the file uploaded, you will probably want to adjust the size of the picture before posting. You can adjust the height/width in the file upload program. I have found that, very roughly speaking, somewhere around 4-500 height and 5-600 width fits well in the post/screen.
This picture was cropped down to 421KB and the original upload size was 1454 width and 1087 height. I just divided both by 3 and ended up with 484W X 362H.