I haven't seen this discussed, but I figured out why I was having difficulty getting Houzz to upload my photos--and why sometimes it's a problem and other times not a problem! So I'm sharing it here and maybe it can help someone else.

The newer versions of iPhone software now stores photo files as an .HEIC file. They switch to HEIC files because take up less storage space on your phone. The old type of file that we are all used to working with is a .JPG file--pronounced j-peg. It doesn't appear that Houzz accepts these new .HEIC files, but when I convert them to JGPs it's no longer a problem to upload. I also realized that my old files weren't a problem but it was the newer files--photos taken after the software change--that were the problem.

The first part of the solution is to set your iPhone so that it goes back to taking pictures as .JPG files. That works as long as you don't have a limited storage on your phone. Here's how to do that: https://www.softwarert.com/transfer-photos-iphone-to-computer-heic-jpg/ All my photos after I made this change now transfer as JPG photos.

For the second part of the solution the photos that are already HEIC have to be converted before you try to upload them. (For clarification I always transfer photos to my MacBook and participate on the forum from that computer, not my phone) You can use a third party app to do the conversion or as in my case I was able to set my MacBook up to do it as it already has that capability. I won't link instructions as they would be different for different computers, but if you will do a search on the type of computer you use and "HEIF conversion to JPG" you will be able to track down instructions.

I was so frustrated before I figured this out! If everybody else has already figured this out and I'm again late to the party just carry on--maybe it will help in a search for someone down the road.