CHris, I use the free MIHOV download for an image resizer.
Otherwise, WINDOWS has a built in way.....if you're using WINDOWS.
have a picture in a folder. On your desktop is an easy place to play.
COPY it to another name picture, so you have a backup of original, then screw with the backup copy, leave the original alone.
rc on it - the backup copy picture.
You'll get a drop-down list of things you can do.
select EDIT which might be 3rd option from the top.
at top, left area - see crop-resize-rotate - select RESIZE.
see Percentage and Pixels - hit PIXELS radio button.
values shown in boxes horizontal and vertical will show current values.
I use 640 x 480, so 640 on the first value, 480 on the second value
? could probably use 640 x 640 & be ok.
Point is, try it, screw with it, use whatever values work for you, SAVE IT, and get a decent looking shot to put on the forum.
Test it with a test thread, you can always delete it later, after you get it working as you want it to.
AS long as you do the first part right, get a backup copy of your picture, you can't ever go wrong, unless you accidentally delete something LIKE THE ENTIRE FOLDER, haha.