First you want to find a clear case for your phone, This is the one I ordered and I love it. Inexpensive, but works great, it is a true clear not a frosted clear as some are and would obscure your picture, and it is also a rubbery material which I like. Very easy to hold, doesnt block the charger slot of any other aspects of the phone, and most importantly, you can see your pic perfectly through it.
You then want to chose your photo. I love this black and white one I took of the kids recently. They are both actually looking at the camera and smiling so you know huge success. I use PicMonkey for all of my pics, its amazing. If you want to make one like mine with the pic in the middle and the chevron in the background this is how I did it. First I went to Google and image searched grey chevron, it looks good with everything.Of course you can choose anything for your background. Save that pic and edit it in PicMonkey. This is your main pic, you will want to crop it. In the crop area, click the area where it says No Fixed Proportions. This will give you a menu of fixed sizes. One of them is iPhone 5, chose that. Now in the left side menu chose Overlays. At the top it will say "chose your own". You then chose the pic you want to add to it. It will show up small, you can adjust the size of it to how you want and situate it how you want on your background. I then chose the text feature, picked one I liked and did my kids initials. You can make it as large as your want and arrange it whereever. Now if you just want a pic on your phone case, no other background, text, etc. you can just do the first step uploading your pic to PicMonkey and then cropping that pic to either iPhone or iPhone 5 size depending on which one you have. Keep in mind when choosing a pic you will have to cut out the hole for the camera opening so dont choose a picture that will be messed up by removing that part of it. When your pic is all done save it. Something I have noticed with PicMonkey, or maybe its just my computer, when you save the name of your pic, type .jpg at the end of the pic name. If you dont, it will ask you if they can do it for you and for some reason it doesnt save it right and just spins and spins. If you dont remember to do it and they ask you, just hit cancel, then save it one your own with the .jpg at the end.
So now you have your picture, you just need to print it out. I use Microsoft Publisher for these things, its very user friendly. Open a new Publisher file and insert the pic onto the page. Now the actual size you want for your picture to fit into the iPhone 5 case is 4 1/4 by 5 7/8. For the iPhone 4 its 2 1/4 by 4 1/2. You may need to play with your pic to make it fit perfect in that, a lil crop here or there but not much. Now I went ahead and made several case pics and inserted them all on this document to print out at once. Then when you want to change them out you have a lot. I used soft gloss or matte photo paper but I think any type of photo paper would be fine.
Now that you have your case inserts printed out, you need to cut it out. Go ahead and cut it out as is, and then round the edges with your scissors to the shape of the case. Go ahead and place your insert into the case and using a pencil draw around the camera hole. I use one of those small razor blades that is on a pen like handle to cut it out. Once thats done, SHAZAM you have your insert! Pop it on it and your case looks great. Now you dont have to just do this with the computer. You can get scrapbook paper and cut it to size and use it. Mod Podge a pic you like onto scrapbook paper and stick it in there. As long as its reasonably flat, stick whatever you like on in there. Within reason.....