Here are the specifications for allowed attachments to posts
Max total size of attachments per post: 8384 KB
Max size per attachment: 4096 KB
Max number of attachments per post: 4
Acceptable file formats: doc,gif,jpg,jpeg,mpg,pdf,png,txt,zip,tif
Maximum dimension on any side: 1202 pixels (800 is preferred; 1201 to open in a new tab...)
Should you need to attach larger images, please post off-site and provide a link.