Based on your query, I would recommend Gradescope as it seems to be the most suitable tool for your needs.

Gradescope allows teachers to grade both individual student assignments and exams uploaded by instructors. This feature could be particularly useful for your need to handle digital solutions for exam images. The tool's AI-Assisted Grading feature can help grade written exams and homework, potentially saving you a lot of time and ensuring consistency in grading.

Moreover, Gradescope offers a dynamic point adjustment rubric, which allows for on-the-fly changes to rubric items and values during grading. This could provide you with the flexibility to adjust grading criteria as needed.

Finally, Gradescope integrates well with learning systems like Canvas and Brightspace, making it simple to add class rosters and push grades to these systems. This could streamline your workflow and make managing your class more efficient.

Remember, Gradescope offers a free basic plan that includes dynamic rubrics, basic assignment types, statistics, and a student mobile app. This could be a cost-effective solution for your needs.