JAMA Requirements for submission of digital images:
Reference https://jamanetwork.com/journals/jama/pages/instructions-for-authors#SecFigures for complete list of details.

To display clinical findings, experimental results, or clinical procedures, including medical imaging, photomicrographs, clinical photographs, and photographs of biopsy specimens. Legends for photomicrographs should include details about the type of stain used and magnification. Required minimum resolution for publication: ≥350 ppi
Acceptable File Formats for Initial Submission: .eps, .jpg, .pdf, .ppt, .psd, .tif
Acceptable File Formats for Revision and Publication: .eps, .jpg, .psd, .tif

Figures may be submitted in electronic format. All images should be at least 5 inches wide. Images should be provided in TIF, EPS, or JPEG format. Graphics software such as Photoshop and Illustrator, not presentation software such as Microsoft Word, PowerPoint, CorelDraw, or Harvard Graphics, should be used in the creation of the art. Color images must be CMYK and at least 300 DPI. Gray scale images should be at least 300 DPI. Combinations of gray scale and line art should be at least 1200 DPI. Line art (black and white or color) should be at least 1200 DPI.

Guidelines for Dermatologic Surgery submissions:
All figures must be submitted electronically according to the specifications outlined below. Failure to submit images according to these specifications will result in reproductions that are small and illegible or in images that are declined.

Figures must depict the results accurately. They must be easily understandable. The legends and headings must accurately reflect the content of the images.

1. Color photographs should be saved in CMYK as TIF or JPG files at 300 dpi at 5 inches in width.

2. New line drawings should be prepared in PowerPoint without embedded images from other sources.

3. Existing line drawings should be scanned at 1200 dpi at a minimum of 12.5 cm (5 in) in width and saved as EPS files (flow charts must not exceed 7 inches [18 cm] in width).

Table to compare Mega Pixel setting as they correspond to resolution:

Optimal image size for PACS upload, 1.8 - 3.0 megapixel, 1 megabyte file size, no compression.