I'm horrible with computers, but this is what I do. Highlight the thumbnail, then do Apple+shift+E. In the "Export Photos" window click on "Scale photos no larger than" and make it the size you want. Click "Export". In the next window make the destination ("Where:") your Desktop. Find the new file on your desktop and click it once so it's highlighted. Do Apple+I. When the info window pops up, look at the size. For the gallery, make sure it is no larger than 150 kb. For an attachment on the forum, you can make it somewhat larger. If it isn't the size I want, I go back through the export process and change the size in the "Export Photos" window. The forum tools can allow this file to then be grabbed and imported from your desktop. BTW, I've learned pretty quickly how big to size my photos, based even on the type of picture. They can be MUCH bigger when they're blurry/bokehful.
