The process as I do it comes in about 4 steps, as follows:
Step 1-Finding Images:
Usually I look for images in one of two sorts of places. Either photobucket, the website where I first started finding images and where I first posted captions. It's the only image upload site of its kind that I know of which is searchable, and it isn't hard to find some decent images with a search like "anime girl", or possibly something more specific if one is looking for it. The other place, and the one I use more prevalently these days, is anime image boards. These are places such as safebooru.org where people primarily post anime images of females, and I'm sure it's obvious why that's useful to me.
I usually look through the images I find, and save all of the ones that I think might have the potential to become a caption into some folders, my own little image archive.
Step 2-Finding Ideas:
This is pretty simple. I look through the image archive, which has long since become rather large, and see if any images put a story into my head. If I can come up with a good premise for an image, it gets moved to a folder and a note of the idea is saved in txt format next to it.
Step 3-Writing Captions:
In the folder of images I've had ideas for, I'll look at the ideas and see if I can write them out into the prose you see as captions. This is the step that always takes the longest, both to feel like writing and the time it takes to do the writing itself. I have at least a few potential captions still in that folder from well over a year back. If I'm not posting any captions, it's probably because I'm just not hitting on the sort of inspiration I need for them, possibly compounded by not having enough time to write them when I do have some inspiration. Sometimes it's even worse--I'll have a caption half or mostly written, and read back over it and find I really dislike it. Sometimes I can salvage this, revising what I don't like or even rewriting the caption entirely; other times it just stays in limbo forever.
Step 4-Putting caption to image:
Once I have a caption written in a text file, I copy and paste it into a word document for a quick spellcheck and then use an image editor (I used to use mspaint, these days I use photoshop) to put the caption into a picture with the image. Then I find a good title for it, save the image and post it online.
That's what I do to make captions. Now, as something of a bonus, I'm going to give you an example of a caption that has been in limbo for quite some time now; I'm not really certain if it's any good or not, but there is definitely something I didn't like about it. I'm posting this one because I've sort of marked it as the one I don't think is ever going to get fixed. Just, as you read it, bear in mind that it was written at least a year ago and I'm not satisfied with it myself.
Below follows the image, and the proposed caption:
Jay had a favorite camping spot. It was on the inside of a good, thick forest, though not so far from civilization as to be unbearable or hard to leave in case of an emergency. It had a well with perfectly pure water that had been around for a long time and still showed no sign of going dry, a beautiful waterfall visible from the campsite..and the best part was that he owned the land it was on!
One weekend he went to his campsite as usual, and spent the day gathering sticks, finding wild fruit, and hunting down a couple of animals. That night he got out of his clothes and put on a white bathrobe he often used out here because it was comfortable, but too thin to be really useful in the colder climate where his house was. The moon was full and lovely in the night sky, he noticed, while going to get some water from the well.
He lowered the bucket, and pulled it up like usual, but when he went to get it off of the tracks he somehow managed to jerk it quite a bit too hard, causing the majority of the water to splash all over him.
He set down the bucket, figuring this was no big deal. He wouldn't freeze to death, after all, and could go and dry off, change into a different bathrobe and hang this one...
But then he started to notice something odd. The bathrobe was stuck to him, of course, being wet, but it seemed like it was getting tighter around his stomach and looser almost everywhere else. And he was getting shorter--the trees around seemed to tower higher by the second. He looked around, trying to remove the disorientation. He felt more weight on his back; it felt like wet hair.
But his hair was supposed to be short.
He looked down at himself and found that his stomach had gotten much thinner. His hips felt a bit wide, and his legs seemed to grow out near the middle; they seemed to squeeze something between them, but then it disappeared, leaving an odd hole. He moved his hand to feel there, trying to determine what had just happened, and found that his arm had become extremely thin, his fingers small and smooth.
Then, still looking down, he saw his chest starting to rise. It usually rose and fell a little bit with every breath he took, especially now, with something strange and unidentifiable going on, but now it seemed unable to fall. Instead it just grew and grew, two bumps which soon became large enough to push apart the already-loose bathrobe, exposing wet skin that was strangely smooth and a bit pale.
Slowly she raised a hand up to her face, brushing a bit of wet hair away from an eye, and picked up the bucket. She would need water, one way or another, right?
It was strange, how as it dawned on her what had happened, it didn't seem at all odd. In fact, it seemed right...she should be called Jamie from now on. This really was a great campsite...