Fix misshapen images
Believe it or not, there are numbers of old (1830s and 1840s) certificates that are not fully rectangular. They are frequently skewed, meaning the sides are parallel and the tops and bottoms are parallel, but they are not quite at right angles. The shapes are hard to notice until one is straightening and trimming for display. I am left to wonder, "What's up with that?"
I don't have good explanations for those oddities. However, misshapen and distorted images of certificates seen on eBay are easier to explain. Collectors who use scanners will seldom encounter such problems, but they are the normal course of business when dealing with camera images.
Why fix at all?
I may never encounter good scanned images of rare certificates during my lifetime. Therefore, I fix a lot of distorted camera images so I can display certificates in the database.
I admit that EBay sellers are among a limited number of people who might need arcane knowledge of how to make camera images sufficiently attractive for display in auction listings. Even then, one would need to balance the amount of time spent on repairs versus the potential additional profit that could be gained. For those people I have made a couple tutorials on fixing distorted images:
How much time to fix?
That all depends on how much practice someone has. The image above right is typical of many eBay images. This image would be easy to repair because the edges are almost straight. If I ignored the slight bend in the righthand edge, I could fix this in two to three minutes. The image would be back in rectangular shape although the proportions of height to width would not be perfect. To achieve that would take another three or four minutes. If I were selling this certificate, and considering this certificate's potential value, I would probably go with the 2-3 minute "good enough" image if I did not own a scanner.
But some certificates are more valuable AND more distorted
True, true, true.
The image at right is equally typical of many ebay images, although perhaps a little better than some. The top and bottom edges are straight and that would be a definite plus. Removing the curve in the left side would take about a minute and the right side just a little longer. All in all, it should take only six or seven minutes to remove distortion in this photo.
The certificate shown was nice and flat, so it would be dramatically easier to fix than images of certificates that had been folded. Distortions can be removed fairly well If sides have two curves (like gentle S-bends) or maybe even three. Throw a fold into the mix, and not only are we talking about a lot of time, but repair might not be worth the effort.
Lots and lots of photo editing software has features for distorting images in (supposedly) artsy ways. Twirls and swirls and inventive distortions are real nifty the first few times they're used. After a few minutes, though, ordinary mouse-drivers are left to wonder how they can put such effects to good use. Especially more than once.
It takes special software to go the other direction and un-distort. If a process like this is important, I advise not acquiring software lacking such capabilities. Both Photoshop and GIMP do what I have suggested above. Sometimes, it might be better to use a photo editor in conjunction with vector-based software such as Adobe Illustrator and CorelDraw. I strongly, strongly, strongly suggest downloading and using a trial version for real work before you buy.