Before sending your photos, it's important to ensure that they meet the minimum size requirement of 500x500 pixels. Here's how you can check the size of your photos on iOS and Android devices:

For iOS Devices:

1. Open the Photos app on your iOS device.
2. Navigate to the photo you want to check.
3. Tap on the photo to open it.
4. Swipe up on the photo or tap the "i" (information) button to reveal details about the photo.
5. The photo information pane will show various details including the dimensions of the photo (e.g., "1024 x 768"). Ensure that both values are 500 or greater.

For Android Devices:

1. Open the Gallery app or any photo viewer app that you use on your Android device.
2. Locate and tap on the photo you wish to check.
3. Once the photo is open, tap on the Menu button (this might appear as three vertical dots or an "i" icon depending on your Android version and device).
4. Choose 'Details' or 'Info' from the menu to view the photo's information.
5. Look for the size of the image displayed in pixels (e.g., "1024x768"). Confirm that the dimensions are at least 500x500 pixels.

Note: On some Android devices, you may also find the dimensions by selecting the photo in the Gallery and looking at the information provided at the top or bottom of the screen without going into a separate menu.

If your photos do not meet the minimum size requirement, you may need to choose a different photo or edit the photo to increase its size, keeping in mind that artificially enlarging a photo may reduce its quality.