...can read, you have to create hidden links, and remember where you put them. The simplest way is to use any old image-editing tool (Paintbrush works fine) to create a tiny image, say, 10 by 10 pixels, that's the same color as the background...

...focus on a specific part of the photo and get rid the extraneous stuff that finds its way into your pictures. Most image editing tools let you select a part of the photo and remove everything outside it with one or two easy steps. Next on the list...