Apple's iPhone photos are currently in the HEIC (high-efficiency image coding) format, an unusual file type that not every app/software support at the moment. If you do not want to use this standard, such as when editing images, you can change the format in Camera settings. Just open "Settings", find "Camera", and then tap "formats". Finally, select "most compatible". This will also allow your videos to come out as H.264 instead of HEVC.
Gary has an iMac, and there's a large percentage of JPGs he can't preview. What is that all about? Leo says if the dimensions read "0" by "0", then the Mac thinks that the files are damaged and need to be repaired, even though Gary can read them on a PC. He should try opening them in Preview first. If he can read them there, then he can export them. Gary can also open them in Picasa, and so Leo suggests exporting them out from there. That can fix them and the Mac apps should be able to open them from there.
Marty is conflicted over whether to scan to the TIFF file format or not. What's the best setting to do scans of images and documents? Leo says that there are two basic categories of image format: Lossless (every bit of data) or Lossy (compressed). TIFF is ideal as a lossless format, as are Bitmaps and PNGs (but compressed). JPEGs and GIFs are compressed or lossy. If he wants to future proof his scans, then lossless TIFF is still the king. Bitmap and PNG will also be around for awhile, though. Image formats will be supported for a long time.
Jim wants to enter pictures in a photo show and the show wants them as JPEGs at 72 dpi. He has to scan his images to do it. Leo says that 72 dpi is at very low quality and it's obviously an online gallery. But he can scan his images at the highest resolution possible and save it in TIFF. That would be lossless compression. He can always open it in a photo editor and then lower the resolution to JPEG. Leo recommends Irfanview.
Caleb loves photography and he's serious about it as a hobby. But he wants to know about shooting in raw. What is that? Leo says that's where the camera doesn't compress any of the data or process it. It just writes the raw image and it usually covers the entire area of the sensor. But in order to look at it, you have to process it later with a program that can understand the data and render it into an image. But Caleb can also choose to save as JPEG to save on space. But it's also considerably compressed. JPEG is only good if you don't want to post process it and color correct it.