Both attempts were using images with too large a cache? That is why they were refused! When I get unlazy, I will play around with the cropping tool to reduce the overall picture and see if they can be accommodated, but I think it is far too large to get down to the max of 128? from the 750 range.
Assuming you mean 128KByte down from 750KByte. I just use flickr and send 1 & 2 megabyte photo up using a desktop uploader (mac ).
Flickr has goofy warning about using it as a bucket. If I set all screen shot and photos to be not shown on flickr home page and exempt from both api and flickr search a person has to go to the photostream url to see them.
In show all sizes you get copy&paste static addr that is not your photostream addr. I also set the uploader to NOT resize for web -- I may buy a Pro account. Lastly, I don't post enough to high volume pages to get on any radar. It is free.