Two things come to mind with the yellow leaves - either too much sun or damage to the roots causing die off. Too much sun seems most likely, since you moved it outside it might be a bit stressed? However, don't change too much until others with more experience with Oncidiums weigh in. I do know that spots on their leaves are not uncommon, I've had quite a bit of trouble with that myself. I find I don't water mine enough (its dry in Eastern WA) and, even though my humidity is low, I guess my air flow isn't as good as it ought to be. I had to spray them with Physan 20 to stop further damage. It seems to be working, time to spray again soon I think.
As far as pictures, be sure the pixel dimensions are no more than 700 pixels either way. I use the preview function of windows and tell it to "open" the picture with Paint. There is a resize button in Paint that I can click a spot for "pixel", then I enter 700 in the biggest number and "ok". That takes care of the size problem for me. I use "save as" and rename it so I don't change the original. In fact I made a folder just for pictures to upload, where the resized ones go.
From the reply page, where I am now, I click "Go Advanced". It has lots of options, I scroll down quite a ways to "Manage Attachments" and click that. That makes another window open (sometimes it is not on top, so keep that in mind). There is an "add files" button, click that. You should see a small "browse" button, that allows you to browse your computer for the pictures you just resized. If you want to add more pictures, there is a plus sign right next to browse to get more pictures. Once you upload them, they will add themselves to your post and be available should you want to use them again later too (by drag and drop).
I know this isn't that simple, its not a simple process unfortunately. You do get used to it though and its very helpful to be able to post pictures when you have a problem and fun to show off your blooms!