Photos do have file size (up to about 2 MB per photo is OK) and physical size limitations for upload, that are placed by the system. That's so we don't get massive photos uploaded to the site that take up tons of storage space and are processor-intensive to display.
Often, smart-phones such as the iPhone are set to take quite large physical and file-size photos, and so they have to be re-sized before uploading or else the upload will fail.
I agree with Arnt - it is always preferable to upload photos to the site and host them here, than to link to an external photo hoster such as Photobucket. People add and remove photos all the time at photo hosters, or accounts change or get removed, and then the photos are lost forever. It's quite easy to upload photos to the site here and we have plenty of storage space available.
If you have problems uploading photos, you can always e-mail them to a system admin (GSXR, Glen or myself) and we can attach them to a specific post, or you can make them available to one of us on a site like DropBox, and we can download/resize/upload the photos to the site. I do this with some regularity for folks who have problems.
Cheers,
Gerry