If a photo imports into TrialPad with the incorrect orientation, and possibly distorted or stretched, it is likely because of the orientation of the device that was used to take the photo. For example, regardless of the orientation you hold a mobile phone to take a photo (portrait or landscape), the images are all saved in one orientation. So there may be one orientation in which the photos are soft-rotated compared to the others, and these will be the ones causing issues, it will be either all the landscape or all the portrait images, from that particular device.
The solution is to rotate those images before importing them (e.g. rotating the photo -90 degrees on your desktop computer), and then import them into TrialPad, you should then be able to rotate them to the correct orientation in TrialPad without them being distorted (the thumbnail image will update after you exit and reopen the folder). Another solution would be to import the photos into the Photos app on your iPad where they should appear correctly, then import them into TrialPad where they should appear without looking stretched or distorted (you still may need to rotate them 90 degrees to be in the correct orientation).