I use a Photoscape X, but I imagine your app can do the same as mine. The best way I've found is to reduce the image in size to about 480 pixels high by 640 pixels wide, and then save the image at around 80-100 KB. If your photos are in a more widescreen format, then I reduce the height of the image to 480 and just let the program maintain the correct ratio (my photos taken with a cell phone usually end up being 480 high by something like 800 wide).
When I post photos after that sort of editing, they appear just the right size to retain a lot of detail, but still be small enough to not have any bandwidth problems.
The attached photo was taken with a Canon SX120is point and shoot camera. The original photo was 4608 pixels wide by 3456 pixels high, and the image was 4.77 MB. I reduced it on photoscape X to 480 pixels high by 640 pixels wide, and saved it at 90KB.
That's the resulting image. You could play around with the size if you wanted it to be larger. You can always preview the image in your posting before you actually post it, and see how it's going to look.
As an experiment, I took the above photo and re-edited it on Photoscape X. I enlarged the 480 x 640 image at 90 KB to 700 x 933 at 142 KB, and this is how it looks. If the image loses some detail, you can try saving it in a larger file size. I don't know what the cutoff in here is for file size; I still go by the recommendations for posting photos that were in place a long time ago when I posted a lot on the Stromtroopers forum.
