almost none of the pics used for captions are taken by the caption-er. As long as you credit the source, and don't make money off it, you should be fine. But you need to respect if a photographer/copyright holder tells you not to distribute.

Another option would be to use public domain images.  



In addition to what I have said before:

Another way to get around any legal hassle is to re-draw images yourself. I am not joking, for example in one of my songs (and you might wonder why you hear this kind of thing in a lot of songs) I use a bass line which is sooooooo from a technotronic (might be misspelled) song. However because I played it myself, and created the bass waves myself, even though they are the same notes, because I am re-creating it and not sampling it, it is totally legal. Now if I were to use that bass line throughout my entire song (which I do not since it is a jumble of re-made retro lines) and that bass line were to be legally proved in court to be the heart of the origional song and to be considered the heart of my song, they could make grounds to take some % of my profits *rofl*. Music and video medias though are a lot more picky than single picture medias. I honestly think the best thing you can do is to keep the pic the same size, and only modify one thing, the jpeg compression quality. Take it down to like 65% and I highly doubt anyone would go after you for using it. It won't look like crap, but it will sure look a lot more like a jpeg from the 90s and at the most you will get hassled to remove it.

So getting back to cappys, if you make a cappy in which you copy say an anime drawing by looking at a print of it, and then re-draw it yourself on the PC, unless the character is trademarked, you are 100% in the clear. If it is a trademarked character, it is best not to use the trademarked name for them when you make the cappy.

I mean honestly, unless you start up a website, stealing pics off the net from all places, and then make them into cappys and charge to get them, as well as keep them in a high quality format, the kind of community is sooooo small who even reads them or knows that they exist, that it would be hard for someone to claim loss of sales of a product due to your use of the pic in your cappy. Oh and that is also one of the most important factors, to actually sue you, they do have to prove that your use of their material hurt their sales or profits in some signifigant way. (I really looked into this when I considered using a few voice samples from a movie for like weeks to be totally sure about US copyright law and how it is practiced) Either that or they have to prove that you have benifitted in some finacial way. So as long as they can do neither, and you removed the material from the net (if asked), you are pretty safe.