I have another easy way.
Download a free software from a Japanese website
http://no722.cocolog-nifty.com/blog/
You can use the software in English. Although there is no English version of the page.
The file name is called "ChainLP036b6.zip". Just click on it to download.
Install & Run the software.
Then put all the image file into a folder(format can be jpg, png), click file--> open sequential file. Choose the folder where you place the files.
You can set the size of the output file as you like. Choose ePu if you want epub output.
Other choices of output file include pdf & lrf files.
Then you can click the 'output' button.
This convert the images into a ePub file. Done.