Every office has its own requirements, in addition to the laid down requirements for instance I have to have a Thai witness to my application, and I have to submit his/her details and copy his house book. Additionally I have to produce a bank book with 100,000 baht in it, which I am informed is increasing to 200,000B this year. So my advice pay them a visit and ask for all details prior to application
Always check with the Immigration Office where you are completing your extension for requirements. Pay a visit and ask saves many other visits. Every Office has its own quirky rules. For instance, where I do mine, they require to see my bank book showing minimum 100,000
Have extended by this method many times now, sometimes they visit other times not, last time they did not require the photographs, everywhere different, Here i am required to show my bank book showing at least 100,000B in it, There nothing about this on the requirements
I have been extending my visa via the monthly income system for years now. My Thai bank print off the monthly income on individual sheets for each month and I collect them from the bank having first arranged it with the bank, then take them with me when I visit the office for my extension